Dental compositions comprising ethylenically unsaturated addition-fragmentation agent

ABSTRACT

Dental compositions are described comprising an addition-fragmentation agent comprising at least one ethylenically unsaturated terminal group and a backbone unit comprising an α,β-unsaturated carbonyl; at least one monomer comprising at least two ethylenically unsaturated group; and inorganic oxide filler. The addition-fragmentation agent is preferably free-radically cleavable. The addition-fragmentation agent preferably comprises at least two ethylenically unsaturated terminal groups, such as (meth)acTylate groups. In some embodiments, the addition-fragmentation agent has the formula: wherein R 1 , R 2  and R 3  are each independently Z m , -Q-, a (hetero)alkyl group or a (hetero)aryl group with the proviso that at least one of R 1 , R 2  and R 3  is Z m -Q-; Q is a linking group have a valence of m+1; Z is an ethylenically unsaturated polymerizable group; m is 1 to 6; each X1 is independently —O— or —NR 4 —, where R 4  is H or C 1 -C 4  alkyl; and n is 0 or 1. Also described are dental articles prepared from a dental composition comprising an addition-fragmentation agent and methods of treating a tooth surface.

SUMMARY

Although various hardenable dental compositions have been described,industry would find advantage in compositions having improved propertiessuch as reduced stress deflection and/or reduced shrinkage whilemaintaining sufficient mechanical properties and depth of cure.

In one embodiment a dental composition is described comprising anaddition-fragmentation agent comprising at least one ethylenicallyunsaturated terminal group and a backbone unit comprising anα,β-unsaturated carbonyl; at least one monomer comprising at least twoethylenically unsaturated group; and inorganic oxide filler. Theaddition-fragmentation agent is preferably free-radically cleavable. Theaddition-fragmentation agent preferably comprises at least twoethylenically unsaturated terminal groups, such as (meth)acrylategroups. In some embodiments, the addition-fragmentation agent has theformula:

-   -   wherein    -   R¹, R² and R³ are each independently Z_(m)-Q-, a (hetero)alkyl        group or a (hetero)aryl group with the proviso that at least one        of R¹, R² and R³ is Z_(m)-Q-;    -   Q is a linking group have a valence of m+1;    -   Z is an ethylenically unsaturated polymerizable group;    -   m is 1 to 6;    -   each X¹ is independently —O— or —NR⁴—, where R⁴ is H or C₁-C₄        alkyl; and    -   n is 0 or 1.

In another embodiment, a dental article is described comprising ahardenable dental composition comprising an addition-fragmentation agentas described herein at least partially hardened.

In other embodiments, methods of treating a tooth surface are described.In one embodiment, the method comprises providing a hardenable dentalcomposition comprising an addition-fragmentation agent as describedherein; placing the dental composition on a tooth surface in the mouthof a subject; and hardening the hardenable dental composition. Inanother embodiment, the method comprising providing an at leastpartially hardened dental article comprising an addition-fragmentationagent as described herein, and adhering the dental article on a toothsurface in the mouth of a subject.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 depicts a machined aluminum block utilized as a sample holder fora curable composition during Stress Deflection testing.

FIG. 2 depicts a Stress Deflection testing apparatus.

DETAILED DESCRIPTION

As used herein, “dental composition” refers to a material, optionallycomprising filler, capable of adhering or being bonded to an oralsurface. A curable dental composition can be used to bond a dentalarticle to a tooth structure, form a coating (e.g., a sealant orvarnish) on a tooth surface, be used as a restorative that is placeddirectly into the mouth and cured in-situ, or alternatively be used tofabricate a prosthesis outside the mouth that is subsequently adheredwithin the mouth.

Curable dental compositions include, for example, adhesives (e.g.,dental and/or orthodontic adhesives), cements (e.g., resin-modifiedglass ionomer cements, and/or orthodontic cements), primers (e.g.,orthodontic primers), liners (applied to the base of a cavity to reducetooth sensitivity), coatings such as sealants (e.g., pit and fissure),and varnishes; and resin restoratives (also referred to as directcomposites) such as dental fillings, as well as crowns, bridges, andarticles for dental implants. Highly filled dental compositions are alsoused for mill blanks, from which a crown may be milled. A composite is ahighly filled paste designed to be suitable for filling substantialdefects in tooth structure. Dental cements are somewhat less filled andless viscous materials than composites, and typically act as a bondingagent for additional materials, such as inlays, onlays and the like, oract as the filling material itself if applied and cured in layers.Dental cements are also used for permanently bonding dental restorationssuch as a crown or bridge to a tooth surface or an implant abutment.

As used herein:

“dental article” refers to an article that can be adhered (e.g., bonded)to a tooth structure or dental implant. Dental articles include, forexample, crowns, bridges, veneers, inlays, onlays, fillings, orthodonticappliances and devices.

“orthodontic appliance” refers to any device intended to be bonded to atooth structure, including, but not limited to, orthodontic brackets,buccal tubes, lingual retainers, orthodontic bands, bite openers,buttons, and cleats. The appliance has a base for receiving adhesive andit can be a flange made of metal, plastic, ceramic, or combinationsthereof. Alternatively, the base can be a custom base formed from curedadhesive layer(s) (i.e. single or multi-layer adhesives).

“oral surface” refers to a soft or hard surface in the oral environment.Hard surfaces typically include tooth structure including, for example,natural and artificial tooth surfaces, bone, and the like.

“hardenable” and “curable’ is descriptive of a material or compositionthat can be cured (e.g., polymerized or crosslinked) by heating toinduce polymerization and/or crosslinking; irradiating with actinicirradiation to induce polymerization and/or crosslinking; and/or bymixing one or more components to induce polymerization and/orcrosslinking. “Mixing” can be performed, for example, by combining twoor more parts and mixing to form a homogeneous composition.Alternatively, two or more parts can be provided as separate layers thatintermix (e.g., spontaneously or upon application of shear stress) atthe interface to initiate polymerization.

“hardened” refers to a material or composition that has been cured(e.g., polymerized or crosslinked).

“hardener” refers to something that initiates hardening of a resin. Ahardener may include, for example, a polymerization initiator system, aphotoinitiator system, a thermal initiator and/or a redox initiatorsystem.

“(meth)acrylate” is a shorthand reference to acrylate, methacrylate, orcombinations thereof; “(meth)acrylic” is a shorthand reference toacrylic, methacrylic, or combinations thereof; and “(meth)acryl” is ashorthand reference to acryl, methacryl, or combinations thereof.

“acryloyl” is used in a generic sense and mean not only derivatives ofacrylic acid, but also amine, and alcohol derivatives, respectively;

“(meth)acryloyl” includes both acryloyl and methacryloyl groups; i.e. isinclusive of both esters and amides.

“alkyl” includes straight-chained, branched, and cyclic alkyl groups andincludes both unsubstituted and substituted alkyl groups. Unlessotherwise indicated, the alkyl groups typically contain from 1 to 20carbon atoms. Examples of “alkyl” as used herein include, but are notlimited to, methyl, ethyl, n-propyl, n-butyl, n-pentyl, isobutyl,t-butyl, isopropyl, n-octyl, n-heptyl, ethylhexyl, cyclopentyl,cyclohexyl, cycloheptyl, adamantyl, and norbornyl, and the like. Unlessotherwise noted, alkyl groups may be mono- or polyvalent, i.e monvalentalkyl or polyvalent alkylene.

“heteroalkyl” includes both straight-chained, branched, and cyclic alkylgroups with one or more heteroatoms independently selected from S, O,and N with both unsubstituted and substituted alkyl groups. Unlessotherwise indicated, the heteroalkyl groups typically contain from 1 to20 carbon atoms. “Heteroalkyl” is a subset of “hydrocarbyl containingone or more S, N, O, P, or Si atoms” described below. Examples of“heteroalkyl” as used herein include, but are not limited to, methoxy,ethoxy, propoxy, 3,6-dioxaheptyl, 3-(trimethylsilyl)-propyl,4-dimethylaminobutyl, and the like. Unless otherwise noted, heteroalkylgroups may be mono- or polyvalent, i.e. monovalent heteroalkyl orpolyvalent heteroalkylene.

“aryl” is an aromatic group containing 6-18 ring atoms and can containoptional fused rings, which may be saturated, unsaturated, or aromatic.Examples of an aryl groups include phenyl, naphthyl, biphenyl,phenanthryl, and anthracyl. Heteroaryl is aryl containing 1-3heteroatoms such as nitrogen, oxygen, or sulfur and can contain fusedrings. Some examples of heteroaryl groups are pyridyl, furanyl,pyrrolyl, thienyl, thiazolyl, oxazolyl, imidazolyl, indolyl,benzofuranyl, and benzthiazolyl. Unless otherwise noted, aryl andheteroaryl groups may be mono- or polyvalent, i.e. monovalent aryl orpolyvalent arylene.

“(hetero)hydrocarbyl” is inclusive of hydrocarbyl alkyl and aryl groups,and heterohydrocarbyl heteroalkyl and heteroaryl groups, the latercomprising one or more catenary oxygen heteroatoms such as ether oramino groups. Heterohydrocarbyl may optionally contain one or morecatenary (in-chain) functional groups including ester, amide, urea,urethane, and carbonate functional groups. Unless otherwise indicated,the non-polymeric (hetero)hydrocarbyl groups typically contain from 1 to60 carbon atoms. Some examples of such heterohydrocarbyls as used hereininclude, but are not limited to, methoxy, ethoxy, propoxy,4-diphenylaminobutyl, 2-(2′-phenoxyethoxy)ethyl, 3,6-dioxaheptyl,3,6-dioxahexyl-6-phenyl, in addition to those described for “alkyl”,“heteroalkyl”, “aryl”, and “heteroaryl” supra.

As used herein, “a,” “an,” “the,” “at least one,” and “one or more” areused interchangeably.

Also herein, the recitations of numerical ranges by endpoints includeall numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2,2.75, 3, 3.80, 4, 5, etc.).

DETAILED DESCRIPTION

Presently described are dental compositions, dental articles, andmethods of use. The dental composition comprises at least oneaddition-fragmentation agent. The addition-fragmentation agentcomprising at least one ethylenically unsaturated terminal group and abackbone unit comprising an α,β-unsaturated carbonyl. Theaddition-fragmentation agent is free-radically cleavable.

The addition-fragmentation agents are preferably of the followingformula:

whereinR¹, R² and R³ are each independently Z_(m)-Q-, a (hetero)alkyl group ora (hetero)aryl group with the proviso that at least one of R¹, R² and R³is Z_(m)-Q-,Q is a linking group have a valence of m+1;Z is an ethylenically unsaturated polymerizable group,m is 1 to 6, preferably 1 to 2;each X¹ is independently —O— or —NR⁴—, where R⁴ is H or C₁-C₄ alkyl, andn is 0 or 1.

Addition-fragmentation agents according to Formula I are described inU.S. provisional patent application 61/442,980, concurrently filed Feb.15, 2011; incorporated herein by reference.

In a favored embodiment, the addition-fragmentation materials (“AFM”)may be added to a dental composition comprising at least oneethylenically unsaturated monomer or oligomer. Without intending to bebound by theory, it is surmised that the inclusion of suchaddition-fragmentation material reduces the polymerization-inducedstresses, such as by the mechanism described in U.S. provisional patentapplication 61/442,980. For embodiments wherein the AFM aremultifunctional, comprising at least two ethylenically unsaturated group(e.g. Z is ≧2 in Formula I), the material can function as crosslinkingagents, where the crosslinks are labile.

The ethylenically unsaturated moiety, Z, of the monomer may include, butis not limited to the following structures, including (meth)acryloyl,vinyl, styrenic and ethynyl, that are more fully described in referenceto the preparation of the compounds below.

wherein R⁴ is H or C₁-C₄ alkyl.

In some embodiments, Q is selected from —O—, —S—, —NR⁴—, —SO₂—, —PO₂—,—CO—, —OCO—, —R⁶—, —NR⁴—CO—NR⁴—, NR⁴—CO—O—, NR⁴—CO—NR⁴—CO—O—R⁶—,—CO—NR⁴—R⁶—, —R⁶—CO—O—R⁶—, —O—R⁶—, —S—R⁶—, —S—R⁶—, —NR⁴—R⁶—, —SO₂—R⁶—,—PO₂—R⁶—, CO—R⁶—NR⁴—CO—R⁶—, NR⁴—R⁶—CO—O—, and NR⁴—CO—NR⁴—, wherein eachR⁴ is hydrogen, a C₁ to C₄ alkyl group, or aryl group, each R⁶ is analkylene group having 1 to 6 carbon atoms, a 5- or 6-memberedcycloalkylene group having 5 to 10 carbon atoms, or a divalent arylenegroup having 6 to 16 carbon atoms, with the proviso that Q-Z does notcontain peroxidic linkages.

In some embodiments, Q is an alkylene, such as of the formula—C_(r)H_(2r)—, where r is 1 to 10. In other embodiments, Q is ahydroxyl-substituted alkylene, such as —CH₂—CH(OH)—CH₂—. In someembodiments, Q is an aryloxy-substituted alkylene. In some embodiments,R⁵ is an alkoxy-substituted alkylene.

R¹—X¹— groups (and optionally R²—X²— groups) is typically selected fromH₂C═C(CH₃)C(O)—O—CH₂—CH(OH)—CH₂—O—,H₂C═C(CH₃)C(O)—O—CH₂—CH(O—(O)C(CH₃)═CH₂)—CH₂—O—,H₂C═C(CH₃)C(O)—O—CH(CH₂OPh)—CH₂—O—,H₂C═C(CH₃)C(O)—O—CH₂CH₂—N(H)—C(O)—O—CH(CH₂OPh)—CH₂—O—,H₂C═C(CH₃)C(O)—O—CH₂—CH(O—(O)C—N(H)—CH₂CH₂—O—(O)C(CH₃)C═CH₂)—CH₂—O—,H₂C═C(H)C(O)—O—(CH₂)₄—O—CH₂—CH(OH)—CH₂—O—,H₂C═C(CH₃)C(O)—O—CH₂—CH(O—(O)C—N(H)—CH₂CH₂—O—(O)C(CH₃)C═CH₂)—CH₂—O—,CH₃—(CH₂)₇—CH(O—(O)C—N(H)—CH₂CH₂—O—(O)C(CH₃)C═CH₂)—CH₂—O—,H₂C═C(H)C(O)—O—(CH₂)₄—O—CH₂—CH(—O—(O)C(H)═CH₂)—CH₂—O— andH₂C═C(H)C(O)—O—CH₂—CH(OH)—CH₂—O—.H₂C═C(H)C(O)—O—(CH₂)₄—O—CH₂—CH(—O—(O)C(H)═CH₂)—CH₂—O—, andCH₃—(CH₂)₇—CH(O—(O)C—N(H)—CH₂CH₂—O—(O)C(CH₃)C═CH₂)—CH₂—O—.

The compounds of Formula I may be prepared from (meth)acrylate dimersand trimers by substitution, displacement or condensation reactions. Thestarting (meth)acrylate dimers and trimers may be prepared by freeradical addition of a (meth)acryloyl monomer in the presence of a freeradical initiator and a Cobalt (II) complex catalyst using the processof U.S. Pat. No. 4,547,323, incorporated herein by reference.Alternatively, the (meth)acryloyl dimers and trimers may be preparedusing a cobalt chelate complex using the processes of U.S. Pat. No.4,886,861 (Janowicz) or U.S. Pat. No. 5,324,879 (Hawthorne),incorporated herein by reference. In either process, the reactionmixture can contain a complex mixture of dimers, trimers, higheroligomers and polymers and the desired dimer or trimer can be separatedfrom the mixture by distillation. Such synthesis is further described inU.S. provisional patent application 61/442,980 and the forthcomingexamples.

The concentration of a component of hardenable (i.e. polymerizable)dental composition described herein can be expressed with respect to the(i.e. unfilled) polymerizable resin portion of the dental composition.For favored embodiments, wherein the composition further comprisesfiller, the concentration of monomer can also be expressed with respectto the total (i.e. filled) composition. When the composition is free offiller, the polymerizable resin portion is the same as the totalcomposition.

The polymerizable resin portion of the hardenable (i.e. polymerizable)dental composition described herein comprises at least 0.5 wt-%, or 1wt-%, 1.5 wt-%, or 2 wt-% of addition-fragmentation agent(s). Theaddition-fragmentation agent may comprise a single monomer or a blend oftwo or more addition-fragmentation agents. The total amount ofaddition-fragmentation agent(s) in the polymerizable resin portion ofthe hardenable (i.e. polymerizable) dental composition is typically nogreater than 30 wt-%, 25 wt-%, 20 wt-%, or 15 wt-%. As the concentrationof the addition-fragmentation monomer increases, the stress deflectionand Watts Shrinkage typically decrease. However, when the amount ofaddition-fragmentation agent exceeds an optimal amount, mechanicalproperties such as Diametral tensile strength and/or Barcol hardness, ordepth of cure may be insufficient.

Materials with high polymerization stress upon curing generate strain inthe tooth structure. One clinical consequence of such stress can be adecrease in the longevity of the restoration. The stress present in thecomposite passes through the adhesive interface to the tooth structuregenerating cuspal deflection and cracks in the surrounding dentin andenamel which can lead to postoperative sensitivity as described in R. R.Cara et al, Particulate Science and Technology 28; 191-206 (2010).Preferred (e.g. filled) dental compositions (useful for restorationssuch as fillings and crowns) described herein typically exhibit a stressdeflection of no greater than 2.0, or 1.8, or 1.6, or 1.4, or 1.2 or 1.0or 0.8 or 0.6 microns.

In other embodiments, the inclusion of the addition-fragmentationagent(s) provides a significant reduction in stress even though thestress deflection is greater than 2.0 microns. For example, theinclusion of the addition-fragmentation agent(s) may reduce the stressfrom about 7 microns to about 6, or about 5, or about 4, or about 3microns.

In some embodiments, the total amount of addition-fragmentation agent(s)in the polymerizable resin portion of the hardenable (i.e.polymerizable) dental composition is no greater than 14 wt-%, 13 wt-%,or 12 wt-%, or 11 wt-%, or 10 wt-%.

The filled hardenable (i.e. polymerizable) dental composition describedherein typically comprises at least 0.1 wt-%, or 0.15 wt-%, or 0.20 wt-%of addition-fragmentation agent(s). The total amount ofaddition-fragmentation agent(s) in the filled hardenable (i.e.polymerizable) dental composition is typically no greater than 5 wt-%,or 4 wt-%, or 3 wt-%, or 2 wt-%.

The hardenable (e.g. dental) compositions described herein furthercomprise at least one ethylenically unsaturated monomer or oligomer incombination with the addition-fragmentation agent. In some embodiments,such as primers, the ethylenically unsaturated monomer may bemonofunctional, having a single (e.g. terminal) ethylenicallyunsaturated group. In other embodiments, such as dental restorations theethylenically unsaturated monomer is multifunctional. The phrase“multifunctional ethylenically unsaturated” means that the monomers eachcomprise at least two ethylenically unsaturated (e.g. free radically)polymerizable groups, such as (meth)acrylate groups.

In favored embodiments, such ethylenically unsaturated group is a (e.g.terminal) free radically polymerizable group including (meth)acryl suchas (meth)acrylamide (H₂C═CHCON— and H₂C═CH(CH₃)CON—) and(meth)acrylate(CH₂CHCOO— and CH₂C(CH₃)COO—). Other ethylenicallyunsaturated polymerizable groups include vinyl (H₂C═C—) including vinylethers (H₂C═CHOCH—). The ethylenically unsaturated terminalpolymerizable group(s) is preferably a (meth)acrylate group,particularly for compositions that are hardened by exposure to actinic(e.g. UV) radiation. Further, methacrylate functionality is typicallypreferred over the acrylate functionality in curable dentalcompositions.

The ethylenically unsaturated monomer may comprise various ethylenicallyunsaturated monomers, as known in the art, for use in dentalcompositions.

In favored embodiments, the (e.g. dental) composition comprises one ormore ethylenically unsaturated (e.g. (meth)acrylate) monomers having alow volume shrinkage monomer. Preferred (e.g. filled) dentalcompositions (useful for restorations such as fillings and crowns)described herein comprise one or more low volume shrinkage monomers suchthat the composition exhibits a Watts Shrinkage of less than about 2%.In some embodiments, the Watts Shrinkage is no greater than 1.90%, or nogreater than 1.80%, or no greater than 1.70%, or no greater than 1.60%.In favored embodiments, the Watts Shrinkage is no greater than 1.50%, orno greater than 1.40%, or no greater than 1.30%, and in some embodimentsno greater than 1.25%, or no greater than 1.20%, or no greater than1.15%, or no greater than 1.10%.

Preferred low volume shrinkage monomers include isocyanurate monomers,such as described in WO2011/126647; tricyclodecane monomers, such asdescribed in EP Application No. 10168240.9, filed Jul. 2, 2010;polymerizable compounds having at least one cyclic allylic sulfidemoiety such as described in US2008/0194722; methylene dithiepane silanesas described in U.S. Pat. No. 6,794,520; oxetane silanes such asdescribed in U.S. Pat. No. 6,284,898; and di-, tri, and/ortetr-(meth)acryloyl-containing materials such as described inWO2008/082881; each of which are incorporated herein by reference.

In favored embodiments, the majority of the (e.g. unfilled)polymerizable resin composition comprises one or more low volumeshrinkage monomers. For example, at least 50%, 60%, 70%, 80%, 90% ormore of the (e.g. unfilled) polymerizable resin may comprise low volumeshrinkage monomer(s).

In one embodiment, the dental composition comprises at least oneisocyanurate monomer. The isocyanurate monomer generally comprises atrivalent isocyanuric acid ring as an isocyanurate core structure and atleast two ethylenically unsaturated (e.g. free radically) polymerizablegroups bonded to at least two of the nitrogen atoms of the isocyanuratecore structure via a (e.g. divalent) linking group. The linking group isthe entire chain of atoms between the nitrogen atom of the isocyanuratecore structure and the terminal ethylenically unsaturated group. Theethylenically unsaturated (e.g. free radically) polymerizable groups aregenerally bonded to the core or backbone unit via a (e.g. divalent)linking group.

The trivalent isocyanurate core structure generally has the formula:

The divalent linking group comprises at least one nitrogen, oxygen orsulfur atom. Such nitrogen, oxygen or sulfur atom forms an urethane,ester, thioester, ether, or thioether linkage. Ether and especiallyester linkages can be beneficial over isocyanurate monomers comprisingurethane linkages for providing improved properties such as reducedshrinkage, and/or increased mechanical properties, e.g., diametraltensile strength (DTS). Thus, in some embodiments, the divalent linkinggroups of the iscosyanurate monomer are free of urethane linkages. Insome favored embodiments, the divalent linking group comprises an esterlinkage such as an aliphatic or aromatic diester linkage.

The isocyanurate monomer typically has the general structure

wherein R₁ is a straight chain, branched or cyclic alkylene, arylene, oralkarylene, optionally including a heteroatom (e.g. oxygen, nitrogen, orsulfur); R₂ is hydrogen or methyl; Z is alkylene, arylene, or alkarylenelinking group comprising at least one moiety selected from urethane,ester, thioester, ether, or thioether, and combinations of suchmoieties; and at least one of R₃ or R₄ is

R₁ is typically a straight chain, branched or cyclic alkylene,optionally including a heteroatom, having no greater than 12 carbonsatoms. In some favored embodiments, R₁ has no greater than 8, 6, or 4carbon atoms. In some favored embodiments, R₁ comprises at least onehydroxyl moiety.

In some embodiments, Z comprises an aliphatic or aromatic ester linkagesuch as a diester linkage.

In some embodiment, Z further comprises one or more ether moieties.Hence, the linking group may comprise a combination of ester or diestermoieties and one or more ether moieties.

For embodiments, wherein the isocyanurate monomer is a di(meth)acrylatemonomer, R₃ or R₄ is hydrogen, alkyl, aryl, or alkaryl, optionallyincluding a heteroatom.

R₁ is generally derived from the starting (e.g. hydroxy terminated)isocyanurate precursor. Various isocyanurate precursor materials arecommercially available from TCI America, Portland, Oreg. The structuresof exemplary isocyanurate precursor materials are depicted as follows:

The isocyanurate(meth)acrylate monomers disclosed herein having alinking groups comprising an oxygen atom of an ester moiety weregenerally prepared by reaction of hydroxy or epoxy terminatedisocyanurates with (meth)acrylated carboxylic acids such asmono-(2-methacryloxyethyl)phthalic acid andmono-(2-methacryloxytheyl)succinic acid.

Suitable (meth)acrylated carboxylic acids include for examplemono-(2-methacryloxyethyl)phthalic acid(s),mono-(2-methacryloxytheyl)succinic acid, andmono-(2-methacryloxyethyl)maleic acid. Alternatively, the carboxylicacid may comprise (meth)acrylamido functionally such as methacrylamidoderivatives of naturally occurring amino acids such asmethacrylamidoglycine, methacrylamidoleucine, methacrylamidoalanine etc.

In some embodiments, a single(meth)acrylated carboxylic acid is reactedwith a single hydroxyl terminated isocyanurate (e.g.tris-(2-hydroxylethyl)isocyanurate). When a sufficient molar ratio of(meth)acrylate carboxylic acid is utilized such that all the hydroxylgroups of the ring are reacted, such synthesis can produce a singlereaction product wherein each of the free radically terminated groups,bonded to the nitrogen atoms of the trivalent isocyanuric acid ring, arethe same. However, when a single epoxy terminated isocyanurate isreacted with a single carboxylic acid, the reaction product generallycomprises more than one isomer in the reaction product.

When two different hydroxy or epoxy terminated isocyanurates and/or twodifferent (e.g. (meth)acrylated) carboxylic acids are utilized, astatistical mixture of reaction products are obtained based on therelative amounts of reactants. For example, when a mixture of a(meth)acrylated aromatic carboxylic acid and a (meth)acrylate aliphaticcarboxylic acid are utilized, some of the free radically terminateddivalent linking groups bonded to the nitrogen atom of the trivalentisocyanuric acid ring comprise an aromatic group, whereas others do not.Further, when a combination (e.g. 1 equivalent) of a hydroxyl terminatedcarboxylic acid and (e.g. 2 equivalents) of a monocarboxylic acid (suchas octanoic acid) is reacted with a single hydroxyl terminatedisocyanurate (e.g. tris-(2-hydroxylethyl)isocyanurate), amono(meth)acrylate isocyanurate can be prepared as further described inWO2011/126647. Such mono(meth)acrylate isocyanurate is suitable for useas a reactive diluent.

Alternatively, isocyanurate(meth)acrylate monomers having ether groupcontaining linking groups can be synthesized. For example, in oneillustrative synthesis, phthalic acid anhydride can be reacted with amono-methacrylated di, tri, tetra or polyethylenegylcol in the presenceof a catalytic amount of 4-(dimethylamino)pyridine (DMAP) and butylatedhydroxytoluene inhibitor (BHT) at 95° C. for a 3-6 hours to form amono-methaycrylated polyethyleneglycol phthalic acid mono-ester. Theobtained methacrylated acid can be reacted, in acetone, withtris-(2-hydroxyethyl)isocyanurate using dicyclohexyl carbodiimide (DCC)at 0-5° C. then at room temperature. Such reaction scheme is depicted asfollows:

In another illustrative synthesis, tris(2-hydroxyethyl)isocyanurate canbe reacted with ethylene oxide to form a polyethylene glycol terminatedwith a hydroxyl group. The OH termini can be esterified withmeth(acrylic) acid to provide a product where the linking group is apolyether. Such reaction scheme is depicted as follows:

The isocyanurate monomer is preferably a multi(meth)acrylate such as adi(meth)acrylate isocyanurate monomer or a tri(meth)acrylateisocyanurate monomer.

The di(meth)acrylate monomer has the general structure:

wherein R₁, R₂, R₃ and Z are as previously described; R₆ is a straightchain, branched, or cyclic alkylene, arylene, or alkarylene, optionallyincluding a heteroatom (e.g. oxygen, nitrogen, or sulfur); and Y isalkylene, arylene, or alkarylene linking group comprising at least onemoiety selected from urethane, ester, thioester, ether, or thioether,and combinations of such moieties.

Illustrative di(meth)acrylate isocyanurate monomers includes:

In some favored embodiments, the tri(meth)acrylate monomer has thegeneral structure:

whereinR₁, R₅, and R₆ are independently a straight chain, branched, or cyclicalkylene, arylene, or alkarylene, optionally including a heteroatom(e.g. oxygen, nitrogen, or sulfur); R₂ is hydrogen or methyl; X, Y, andZ are independently alkylene, arylene, or alkarylene linking groupcomprising at least one moiety selected from urethane, ester, thioester,ether, thioether, or combinations of such moieties; and R₂ is hydrogenor methyl.

In some embodiments, R₁, R₅, and R₆ comprise at least one hydroxylmoiety.

Illustrative tri(meth)acrylate isocyanurate monomers include forexample:

The polymerizable resin portion of the hardenable unfilled dentalcomposition described herein may comprise at least 10 wt-%, 15 wt-%, 20wt-%, or 25 wt-%, multifunctional ethylenically unsaturated isocyanuratemonomer(s). The isocyanurate monomer may comprise a single monomer or ablend of two or more isocyanurate monomers. The total amount ofisocyanurate monomer(s) in the unfilled polymerizable resin portion ofthe hardenable (i.e. polymerizable) dental composition is typically nogreater than 90 wt-%, 85 wt-%, 80 wt-%, or 75 wt-%.

In some embodiments, the total amount of isocyanurate monomer(s) in thehardenable unfilled dental composition is at least 30 wt-%, 35 wt-%, or40 wt-% and no greater than 70 wt-%, 65 wt-%, or 60 wt-%.

The filled hardenable dental composition described herein

typically comprises at least 5 wt-%, 6 wt-%, 7 wt-%, 8 wt-%, or 9 wt-%of multifunctional ethylenically unsaturated isocyanurate monomer(s).The total amount of isocyanurate monomer(s) of the filled hardenable(i.e. polymerizable) dental composition is typically no greater than 20wt-%, or 19 wt-%, or 18 wt-%, or 17 wt-%, or 16 wt-%, or 15 wt-%.

In another embodiment, the dental composition comprises at least onetricyclodecane monomer. The tricyclodecane monomer may comprise a singlemonomer or a blend of two or more tricyclodecane monomers. Theconcentration of multifunctional ethylenically unsaturatedtricyclodecane monomer in the (i.e. unfilled) polymerizable resinportion or filled hardenable (i.e. polymerizable) composition can be thesame as just described for the multifunctional ethylenically unsaturatedisocyanurate monomer.

In some embodiments the composition comprises a multifunctionalethylenically unsaturated isocyanurate monomer and multifunctionalethylenically unsaturated tricyclodecane monomer at a weight ratioranging from about 1.5:1 to 1:1.5.

Tricyclodecane monomers generally have the core structure (i.e. backboneunit (U):

In some favored embodiments, the tricyclodecane monomers generally havethe core structure (i.e. backbone unit (U):

Such tricyclodecane monomers can be prepared for example from startingmaterials such as

The backbone unit (U) typically comprises one or two spacer unit(s) (S)bonded to the backbone unit (U) via an ether linkage. At least onespacer unit (S) comprises a CH(O)—OG chain, wherein each group Gcomprises a (meth)acrylate moiety and Q comprises at least one groupselected from hydrogen, alkyl, aryl, alkaryl and combinations thereof.In some embodiments, Q is hydrogen, methyl, phenyl, phenoxymethyl, andcombinations thereof. G may be bonded to the spacer unit(s) (S) via aurethane moiety.

In some embodiments, the spacer unit(s) (S) typically comprise

wherein m is 1 to 3; n is 1 to 3; and Q is hydrogen, methyl, phenyl,phenoxymethyl.

In other embodiments, the spacer unit(s) (S) typically comprise

wherein M=phenyl.

In some embodiments, the tricyclodecane monomer may be characterized bythe structures

wherein for each of these tricyclodecane monomer structures a, b is 0 to3; c, d=0 to 3; (a+b) is 1 to 6; (c+d) is 1 to 6; and Q is independentlyhydrogen, methyl, phenyl or phenoxymethyl.

Some illustrative species of such multifunctional ethylenicallyunsaturated tricyclodecane monomers are described in the followingtable.

TCD-Alcohol—IEM, reaction product of tricyclo[5.2.1.02,6]decanedimethanole (TCD-Alcohol DM) and IEM

The linking groups of the isocyanurate and tricyclodecane monomers aretypically sufficiently low in molecular weight such that the monomer isa stable liquid at 25° C. However, the linking group(s) is typicallyhigher in molecular weight than the oxygen atom of for example2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane (“BisGMA”),a common monomer utilized in dental compositions, that links the(meth)acrylate group to the aromatic ring. The molecular weight of thelinking group(s) of the monomers described is typically at least 50g/mole or 100 g/mole. In some embodiments, the molecular weight of thelinking group is at least 150 g/mole. The molecular weight of thelinking group is typically no greater than about 500 g/mole. In someembodiments, the molecular weight of the linking group is no greaterthan 400 g/mole or 300 g/mole.

In some embodiments, the (i.e. calculated) molecular weight of the lowshrink (e.g. isocyanurate and tricyclodecane) monomers is typically nogreater than 2000 g/mole. In some embodiments, the molecular weight ofthe monomers is no greater than about 1500 g/mole or 1200 g/mole or 1000g/mole. The molecular weight of the monomers is typically at least 600g/mole.

Increasing the molecular weight without forming a solid at 25° C. can beachieved by various synthetic approaches, as depicted above. In someembodiments, the linking groups have one or more pendant substituents.For example, the linking groups may comprise one or more hydroxyl groupsubstituents such an in the case of linking groups comprising alkoxysegments. In other embodiments, the linking groups are branched, and/orcomprise at least one (i.e. aliphatic) cyclic moiety, and/or comprise atleast one aromatic moiety.

In some embodiments, a by-product is formed during the synthesis of themonomer that may be a solid at about 25° C. (i.e. +/−2° C.). Suchby-product is typically removed from the liquid monomer. Hence, theliquid monomer is substantially free of such solid fractions. However,it is contemplated that the liquid monomer may further comprise (e.g.non-crystalline) solid reaction by-products that are soluble in theliquid monomer.

In some embodiments, the dental composition comprises a polymerizablecompound having at least one cyclic allylic sulfide moiety with at leastone (meth)acryloyl moiety.

Such a polymerizable compound is referred to herein as a hybrid monomeror a hybrid compound. The cyclic allylic sulfide moiety typicallycomprises at least one 7- or 8-membered ring that has two heteroatoms inthe ring, one of which is sulfur. Most typically both of the heteroatomsare sulfur, which may optionally be present as part of an SO, SO₂, orS—S moiety. In other embodiments, the ring may comprise a sulfur atomplus a second, different heteroatom in the ring, such as oxygen ornitrogen. In addition, the cyclic allylic moiety may comprise multiplering structures, i.e. may have two or more cyclic allylic sulfidemoieties. The (meth)acryloyl moiety is preferably a (meth)acryloyloxy(i.e. a (meth)acrylate moiety) or a (meth)acryloylamino (i.e., a(meth)acrylamide moiety).

In one embodiment, the low shrinkage monomer includes those representedby the formulae:

In the above formulae, each X can be independently selected from S, O,N, C (e.g., CH₂ or CRR, where each R is independently a H or an organicgroup), SO, SO₂, N-alkyl, N-acyl, NH, N-aryl, carboxyl or carbonylgroup, provided that at least one X is S or a group comprising S.Preferably, each X is S.

Y is either alkylene (e.g., methylene, ethylene, etc.) optionallyincluding a heteroatom, carbonyl, or acyl; or is absent, therebyindicating the size of the ring, typically 7- to 10-membered rings,however larger rings are also contemplated. Preferably, the ring iseither a 7- or 8-membered ring with Y thus being either absent ormethylene, respectively. In some embodiments, Y is either absent or is aC1 to C3 alkylene, optionally including a heteroatom, carbonyl, acyl, orcombinations thereof.

Z is O, NH, N-alkyl (straight chain or branched), or N-aryl (phenyl orsubstituted phenyl).

The R′ group represents a linker selected from alkylene (typicallyhaving more than one carbon atom, i.e. excluding methylene), alkyleneoptionally including a heteroatom (e.g., O, N, S, S—S, SO, SO2),arylene, cycloaliphatic, carbonyl, siloxane, amido (—CO—NH—), acyl(—CO—O—), urethane (—O—CO—NH—), and urea (—NH—CO—NH—) groups, andcombinations thereof. In certain embodiments, R′ comprises an alkylenegroup, typically a methylene or longer group, that may be eitherstraight chain or branched, and which can be either unsubstituted, orsubstituted with aryl, cycloalkyl, halogen, nitrile, alkoxy, alkylamino,dialkylamino, alkylthio, carbonyl, acyl, acyloxy, amido, urethane group,urea group, a cyclic allylic sulfide moiety, or combinations thereof.

R″ is selected from H, and CH₃, and “a” and “b” are independently 1 to3.

Optionally the cyclic allylic sulfide moiety can further be substitutedon the ring with one or more groups selected from straight or branchedchain alkyl, aryl, cycloalkyl, halogen, nitrile, alkoxy, alkylamino,dialkylamino, alkylthio, carbonyl, acyl, acyloxy, amido, urethane group,and urea group. Preferably the selected substituents do not interferewith the hardening reaction. Preferred are cyclic allylic sulfidestructures that comprise unsubstituted methylene members.

A typical low shrinkage monomer can comprise an 8-membered cyclicallylic sulfide moiety with two sulfur atoms in the ring and with thelinker attached directly to the 3-position of the ring with an acylgroup (i.e., Ring-OC(O)—). Typically the weight average molecular weight(MW) of the hybrid monomer ranges from about 400 to about 900 and insome embodiments is at least 250, more typically at least 500, and mosttypically at least 800.

Representative polymerizable compounds having at least one cyclicallylic sulfide moiety with at least one (meth)acryloyl moiety includethe following

The inclusion of a polymerizable compound having at least one cyclicallylic sulfide moiety can result in a synergistic combination of lowvolume shrinkage in combination with high diametral tensile strength.

In another embodiment, the dental composition comprises a low shrinkagemonomer that includes at least one di-, tri-, and/ortetra(meth)acryloyl-containing materials having the general formula:

wherein: each X independently represents an oxygen atom (O) or anitrogen atom (N); Y and A each independently represent an organicgroup, and R¹ represents —C(O)C(CH₃)═CH₂, and/or (ii) q=0 and R²represents —C(O)C(CH₃)═CH₂; m=1 to 5; n=0 to 5; p and q areindependently 0 or 1; and R′ and R² each independently represent H,—C(O)CH═CH₂, or —C(O)C(CH₃)═CH₂. In some embodiments, Y does notrepresent —NHCH₂CH₂— when p=0. Although, this material is a derivativeof bisphenol A, when other low volume shrinkage monomer are employed,such as the isocyanurate and/or tricyclodecane monomer, the dentalcomposition is free of (meth)acrylate monomers derived from bisphenol A.

The multifunctional low shrink monomers (e.g. isocyanurate andtricyclodecane) monomers are (e.g. highly) viscous liquids at about 25°C., yet are flowable. The viscosity as can be measured with a HaakeRotoVisco RV1 device, as described in EP Application No. 10168240.9,filed Jul. 2, 2010; is typically at least 300, or 400, or 500 Pa*s andno greater than 10,000 Pa*s. In some embodiments, the viscosity is nogreater than 5000 or 2500 Pa*s.

The ethylenically unsaturated monomers of the dental composition aretypically stable liquids at about 25° C. meaning that the monomer do notsubstantially polymerize, crystallize, or otherwise solidify when storedat room temperature (about 25° C.) for a typical shelf life of at least30, 60, or 90 days. The viscosity of the monomers typically does notchange (e.g. increase) by more than 10% of the initial viscosity.

Particularly for dental restoration compositions, the ethylenicallyunsaturated monomers generally have a refractive index of at least 1.50.In some embodiments, the refractive index is at least 1.51, 1.52, 1.53,or greater. The inclusion of sulfur atoms and/or the present of one ormore aromatic moieties can raise the refractive index (relative to thesame molecular weight monomer lacking such substituents).

In some embodiments, the (unfilled) polymerizable resin may comprisesolely one or more low shrink monomers in combination with the additionfragmentation agent(s). In other embodiments, the (unfilled)polymerizable resin comprises a small concentration of other monomer(s).By “other” is it meant an ethylenically unsaturated monomer such as a(meth)acrylate monomer that is not a low volume shrinkage monomer.

The concentration of such other monomer(s) is typically no greater than20 wt-%, 19 wt-%, 18 wt-%, 17 wt-%, 16 wt-%, or 15 wt-% of the(unfilled) polymerizable resin portion. The concentration of such othermonomers is typically no greater than 5 wt-%, 4 wt-%, 3 wt-%, or 2 wt-%of the filled polymerizable dental composition.

In some embodiments, the dental composition comprises a low viscosityreactive (i.e. polymerizable) diluent. Reactive diluents typically havea viscosity as can be measured with a Haake RotoVisco RV1 device, asdescribed in EP Application No. 10168240.9, filed Jul. 2, 2010, of nogreater than 300 Pa*s and preferably no greater than 100 Pa*s, or 50Pa*s, or 10 Pa*s. In some embodiments, the reactive diluent has aviscosity no greater than 1 or 0.5 Pa*s. Reactive diluents are typicallyrelatively low in molecular weight, having a molecular weight less than600 g/mole, or 550 g/mol, or 500 g/mole. Reactive diluents typicallycomprise one or two ethylenically unsaturated groups such as in the caseof mono(meth)acrylate or di(meth)acrylate monomers.

In some embodiments, the reactive diluent is an isocyanurate ortricyclodecane monomer. Tricyclodecane reactive diluent may have thesame generally structure as previously described. In favoredembodiments, the tricyclodecane reactive diluent

comprises one or two spacer unit(s) (S) being connected to the backboneunit (U) via an ether linkage; such as described in EP Application No.10168240.9, filed Jul. 2, 2010; incorporated herein by reference. Oneillustrative tricyclodecane reactive diluent has the general structure:

Although the inclusion of an addition fragmentation agent in a lowvolume shrinkage composition typically provides the lowest stress and/orlowest shrinkage, the addition fragmentation agents described herein canalso reduce the stress and shrinkage of dental composition comprisingconventional hardenable (meth)acrylate monomers, such as ethoxylatedbisphenol A dimethacrylate (BisEMA6), 2-hydroxyethyl methacrylate(HEMA), bisphenol A diglycidyl dimethacrylate (bisGMA), urethanedimethacrylate (UDMA), triethlyene glycol dimethacrylate (TEGDMA),glycerol dimethacrylate (GDMA), ethylenegylcol dimethacrylate,neopentylglycol dimethacrylate (NPGDMA), and polyethyleneglycoldimethacrylate (PEGDMMA).

The curable component of the curable dental composition can include awide variety of other ethylenically unsaturated compounds (with orwithout acid functionality), epoxy-functional (meth)acrylate resins,vinyl ethers, and the like.

The (e.g., photopolymerizable) dental compositions may include freeradically polymerizable monomers, oligomers, and polymers having one ormore ethylenically unsaturated groups. Suitable compounds contain atleast one ethylenically unsaturated bond and are capable of undergoingaddition polymerization. Examples of useful ethylenically unsaturatedcompounds include acrylic acid esters, methacrylic acid esters,hydroxy-functional acrylic acid esters, hydroxy-functional methacrylicacid esters, and combinations thereof. Such free radically polymerizablecompounds include mono-, di- or poly-(meth)acrylates (i.e., acrylatesand methacrylates) such as, methyl(meth)acrylate, ethyl(meth)acrylate,isopropyl(meth)acrylate, n-hexyl(meth)acrylate, stearyl(meth)acrylate,allyl(meth)acrylate, glycerol tri(meth)acrylate, ethyleneglycoldi(meth)acrylate, diethyleneglycol di(meth)acrylate, triethyleneglycoldi(meth)acrylate, 1,3-propanediol di(meth)acrylate, trimethylolpropanetri(meth)acrylate, 1,2,4-butanetriol tri(meth)acrylate,1,4-cyclohexanediol di(meth)acrylate, pentaerythritoltetra(meth)acrylate, sorbitol hex(meth)acrylate,tetrahydrofurfuryl(meth)acrylate,bis[1-(2-acryloxy)]-p-ethoxyphenyldimethylmethane,bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane,ethoxylated bisphenol A di(meth)acrylate, andtrishydroxyethyl-isocyanurate tri(meth)acrylate; (meth)acrylamides(i.e., acrylamides and methacrylamides) such as (meth)acrylamide,methylene bis-(meth)acrylamide, and diacetone (meth)acrylamide; urethane(meth)acrylates; the bis-(meth)acrylates of polyethylene glycols(preferably of molecular weight 200-500); and vinyl compounds such asstyrene, diallyl phthalate, divinyl succinate, divinyl adipate anddivinyl phthalate. Other suitable free radically polymerizable compoundsinclude siloxane-functional (meth)acrylates. Mixtures of two or morefree radically polymerizable compounds can be used if desired.

The curable dental composition may also contain a monomer havinghydroxyl groups and ethylenically unsaturated groups in a singlemolecule. Examples of such materials includehydroxyalkyl(meth)acrylates, such as 2-hydroxyethyl(meth)acrylate and2-hydroxypropyl(meth)acrylate; glycerol mono- or di-(meth)acrylate;trimethylolpropane mono- or di-(meth)acrylate; pentaerythritol mono-,di-, and tri-(meth)acrylate; sorbitol mono-, di-, tri-, tetra-, orpenta-(meth)acrylate; and2,2-bis[4-(2-hydroxy-3-ethacryloxypropoxy)phenyl]propane (bisGMA).Suitable ethylenically unsaturated compounds are available from a widevariety of commercial sources, such as Sigma-Aldrich, St. Louis.

The dental compositions described herein may include one or more curablecomponents in the form of ethylenically unsaturated compounds with acidfunctionality. Such components contain acidic groups and ethylenicallyunsaturated groups in a single molecule. When present, the polymerizablecomponent optionally comprises an ethylenically unsaturated compoundwith acid functionality. Preferably, the acid functionality includes anoxyacid (i.e., an oxygen-containing acid) of carbon, sulfur,phosphorous, or boron.

As used herein, ethylenically unsaturated compounds with acidfunctionality is meant to include monomers, oligomers, and polymershaving ethylenic unsaturation and acid and/or acid-precursorfunctionality. Acid-precursor functionalities include, for example,anhydrides, acid halides, and pyrophosphates. The acid functionality caninclude carboxylic acid functionality, phosphoric acid functionality,phosphonic acid functionality, sulfonic acid functionality, orcombinations thereof.

Ethylenically unsaturated compounds with acid functionality include, forexample, α,β-unsaturated acidic compounds such as glycerol phosphatemono(meth)acrylates, glycerol phosphate di(meth)acrylates (GDMA-P),hydroxyethyl(meth)acrylate (e.g., HEMA) phosphates,bis((meth)acryloxyethyl) phosphate, ((meth)acryloxypropyl) phosphate,bis((meth)acryloxypropyl) phosphate, bis((meth)acryloxy)propyloxyphosphate, (meth)acryloxyhexyl phosphate, bis((meth)acryloxyhexyl)phosphate, (meth)acryloxyoctyl phosphate, bis((meth)acryloxyoctyl)phosphate, (meth)acryloxydecyl phosphate, bis((meth)acryloxydecyl)phosphate, caprolactone methacrylate phosphate, citric acid di- ortri-methacrylates, poly(meth)acrylated oligomaleic acid,poly(meth)acrylated polymaleic acid, poly(meth)acrylatedpoly(meth)acrylic acid, poly(meth)acrylated polycarboxyl-polyphosphonicacid, poly(meth)acrylated polychlorophosphoric acid, poly(meth)acrylatedpolysulfonate, poly(meth)acrylated polyboric acid, and the like, may beused as components. Also monomers, oligomers, and polymers ofunsaturated carbonic acids such as (meth)acrylic acids, aromatic(meth)acrylated acids (e.g., methacrylated trimellitic acids), andanhydrides thereof can be used.

The dental compositions can include an ethylenically unsaturatedcompound with acid functionality having at least one P—OH moiety. Suchcompositions are self-adhesive and are non-aqueous. For example, suchcompositions can include: a first compound including at least one(meth)acryloxy group and at least one —O—P(O)(OH)_(x) group, wherein x=1or 2, and wherein the at least one —O—P(O)(OH)_(x) group and the atleast one (meth)acryloxy group are linked together by a C1-C4hydrocarbon group; a second compound including at least one(meth)acryloxy group and at least one —O—P(O)(OH)_(x) group, wherein x=1or 2, and wherein the at least one —O—P(O)(OH)_(x) group and the atleast one (meth)acryloxy group are linked together by a C5-C12hydrocarbon group; an ethylenically unsaturated compound without acidfunctionality; an initiator system; and a filler.

The curable dental compositions can include at least 1 wt-%, at least 3wt-%, or at least 5 wt-% ethylenically unsaturated compounds with acidfunctionality, based on the total weight of the unfilled composition.The compositions can include at most 80 wt-%, at most 70 wt-%, or atmost 60 wt-% ethylenically unsaturated compounds with acidfunctionality. In some embodiments, a curable dental composition isdescribed comprising at least 10 wt-% to about 30 wt-% of ethylenicallyunsaturated compounds with acid functionality, such as a mixture of HEMAand GDMA-P.

The curable dental compositions may include resin-modified glassionomers cements such as those described in U.S. Pat. No. 5,130,347(Mitra) U.S. Pat. No. 5,154,762 (Mitra) U.S. Pat. No. 5,962,550(Akahane). Such compositions can be powder-liquid, paste-liquid orpaste-paste systems. Alternatively, copolymer formulations such as thosedescribed in U.S. Pat. No. 6,126,922 (Rozzi) are included in the scopeof the invention.

An initiator is typically added to the mixture of polymerizableingredients. The initiator is sufficiently miscible with the resinsystem to permit ready dissolution in (and discourage separation from)the polymerizable composition. Typically, the initiator is present inthe composition in effective amounts, such as from about 0.1 weightpercent to about 5.0 weight percent, based on the total weight of thecomposition.

The addition-fragmentation agent is generally free-radically cleavable.Although photopolymerization is one mechanism for generating freeradicals, other curing mechanisms also generate free radicals. Thus, theaddition-fragmentation agent does not require irradiation with actinicradiation (e.g. photocuring) in order to provide the reduction in stressduring curing.

In some embodiments, the mixture of monomers is photopolymerizable andthe composition contains a photoinitiator (i.e., a photoinitiatorsystem) that upon irradiation with actinic radiation initiates thepolymerization (or hardening) of the composition. Suchphotopolymerizable compositions can be free radically polymerizable. Thephotoinitiator typically has a functional wavelength range from about250 nm to about 800 nm. Suitable photoinitiators (i.e., photoinitiatorsystems that include one or more compounds) for polymerizing freeradically photopolymerizable compositions include binary and tertiarysystems. Typical tertiary photoinitiators include an iodonium salt, aphotosensitizer, and an electron donor compound as described in U.S.Pat. No. 5,545,676 (Palazzotto et al.). Iodonium salts include diaryliodonium salts, e.g., diphenyliodonium chloride, diphenyliodoniumhexafluorophosphate, and diphenyliodonium tetrafluoroboarate. Somepreferred photosensitizers may include monoketones and diketones (e.g.alpha diketones) that absorb some light within a range of about 300 nmto about 800 nm (preferably, about 400 nm to about 500 nm) such ascamphorquinone, benzil, furil, 3,3,6,6-tetramethylcyclohexanedione,phenanthraquinone and other cyclic alpha diketones. Of thesecamphorquinone is typically preferred. Preferred electron donorcompounds include substituted amines, e.g., ethyl4-(N,N-dimethylamino)benzoate.

Other suitable photoinitiators for polymerizing free radicallyphotopolymerizable compositions include the class of phosphine oxidesthat typically have a functional wavelength range of about 380 nm toabout 1200 nm. Preferred phosphine oxide free radical initiators with afunctional wavelength range of about 380 nm to about 450 nm are acyl andbisacyl phosphine oxides.

Commercially available phosphine oxide photoinitiators capable offree-radical initiation when irradiated at wavelength ranges of greaterthan about 380 nm to about 450 nm includebis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide (IRGACURE 819, CibaSpecialty Chemicals, Tarrytown, N.Y.),bis(2,6-dimethoxybenzoyl)-(2,4,4-trimethylpentyl) phosphine oxide (CGI403, Ciba Specialty Chemicals), a 25:75 mixture, by weight, ofbis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide and2-hydroxy-2-methyl-1-phenylpropan-1-one (IRGACURE 1700, Ciba SpecialtyChemicals), a 1:1 mixture, by weight, ofbis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide and2-hydroxy-2-methyl-1-phenylpropane-1-one (DAROCUR 4265, Ciba SpecialtyChemicals), and ethyl 2,4,6-trimethylbenzylphenyl phosphinate (LUCIRINLR8893X, BASF Corp., Charlotte, N.C.).

Tertiary amine reducing agents may be used in combination with anacylphosphine oxide. Illustrative tertiary amines include ethyl4-(N,N-dimethylamino)benzoate and N,N-dimethylaminoethyl methacrylate.When present, the amine reducing agent is present in thephotopolymerizable composition in an amount from about 0.1 weightpercent to about 5.0 weight percent, based on the total weight of thecomposition. In some embodiments, the curable dental composition may beirradiated with ultraviolet (UV) rays. For this embodiment, suitablephotoinitiators include those available under the trade designationsIRGACURE and DAROCUR from Ciba Specialty Chemical Corp., Tarrytown, N.Y.and include 1-hydroxy cyclohexyl phenyl ketone (IRGACURE 184),2,2-dimethoxy-1,2-diphenylethan-1-one (IRGACURE 651),bis(2,4,6-trimethylbenzoyl)phenylphosphineoxide (IRGACURE 819),1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propane-1-one(IRGACURE 2959), 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone(IRGACURE 369),2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one (IRGACURE907), and 2-hydroxy-2-methyl-1-phenyl propan-1-one (DAROCUR 1173).

The photopolymerizable compositions are typically prepared by admixingthe various components of the compositions. For embodiments wherein thephotopolymerizable compositions are not cured in the presence of air,the photoinitiator is combined under “safe light” conditions (i.e.,conditions that do not cause premature hardening of the composition).Suitable inert solvents may be employed if desired when preparing themixture. Examples of suitable solvents include acetone anddichloromethane.

Hardening is affected by exposing the composition to a radiation source,preferably a visible light source. It is convenient to employ lightsources that emit actinic radiation light between 250 nm and 800 nm(particularly blue light of a wavelength of 380-520 nm) such as quartzhalogen lamps, tungsten-halogen lamps, mercury arcs, carbon arcs, low-,medium-, and high-pressure mercury lamps, plasma arcs, light emittingdiodes, and lasers. In general, useful light sources have intensities inthe range of 0.200-1000 W/cm². A variety of conventional lights forhardening such compositions can be used.

The exposure may be accomplished in several ways. For example, thepolymerizable composition may be continuously exposed to radiationthroughout the entire hardening process (e.g., about 2 seconds to about60 seconds). It is also possible to expose the composition to a singledose of radiation, and then remove the radiation source, therebyallowing polymerization to occur. In some cases materials can besubjected to light sources that ramp from low intensity to highintensity. Where dual exposures are employed, the intensity of eachdosage may be the same or different. Similarly, the total energy of eachexposure may be the same or different.

The dental compositions comprising the multifunctional ethylenicallyunsaturated monomers may be chemically hardenable, i.e., thecompositions contain a chemical initiator (i.e., initiator system) thatcan polymerize, cure, or otherwise harden the composition withoutdependence on irradiation with actinic radiation. Such chemicallyhardenable (e.g., polymerizable or curable) composition are sometimesreferred to as “self-cure” compositions and may include redox curesystems, thermally curing systems and combinations thereof. Further, thepolymerizable composition may comprise a combination of differentinitiators, at least one of which is suitable for initiating freeradical polymerization.

The chemically hardenable compositions may include redox cure systemsthat include a polymerizable component (e.g., an ethylenicallyunsaturated polymerizable component) and redox agents that include anoxidizing agent and a reducing agent.

The reducing and oxidizing agents react with or otherwise cooperate withone another to produce free-radicals capable of initiatingpolymerization of the resin system (e.g., the ethylenically unsaturatedcomponent). This type of cure is a dark reaction, that is, it is notdependent on the presence of light and can proceed in the absence oflight. The reducing and oxidizing agents are preferably sufficientlyshelf-stable and free of undesirable colorization to permit theirstorage and use under typical conditions.

Useful reducing agents include ascorbic acid, ascorbic acid derivatives,and metal complexed ascorbic acid compounds as described in U.S. Pat.No. 5,501,727 (Wang et al.); amines, especially tertiary amines, such as4-tert-butyl dimethylaniline; aromatic sulfinic salts, such asp-toluenesulfinic salts and benzenesulfinic salts; thioureas, such as1-ethyl-2-thiourea, tetraethyl thiourea, tetramethyl thiourea,1,1-dibutyl thiourea, and 1,3-dibutyl thiourea; and mixtures thereof.Other secondary reducing agents may include cobalt (II) chloride,ferrous chloride, ferrous sulfate, hydrazine, hydroxylamine (dependingon the choice of oxidizing agent), salts of a dithionite or sulfiteanion, and mixtures thereof. Preferably, the reducing agent is an amine.

Suitable oxidizing agents will also be familiar to those skilled in theart, and include but are not limited to persulfuric acid and saltsthereof, such as sodium, potassium, ammonium, cesium, and alkyl ammoniumsalts. Additional oxidizing agents include peroxides such as benzoylperoxides, hydroperoxides such as cumyl hydroperoxide, t-butylhydroperoxide, and amyl hydroperoxide, as well as salts of transitionmetals such as cobalt (III) chloride and ferric chloride, cerium (IV)sulfate, perboric acid and salts thereof, permanganic acid and saltsthereof, perphosphoric acid and salts thereof, and mixtures thereof.

It may be desirable to use more than one oxidizing agent or more thanone reducing agent. Small quantities of transition metal compounds mayalso be added to accelerate the rate of redox cure. The reducing oroxidizing agents can be microencapsulated as described in U.S. Pat. No.5,154,762 (Mitra et al.). This will generally enhance shelf stability ofthe polymerizable composition, and if necessary permit packaging thereducing and oxidizing agents together. For example, through appropriateselection of an encapsulant, the oxidizing and reducing agents can becombined with an acid-functional component and optional filler and keptin a storage-stable state.

Curable dental compositions can also be cured with a thermally or heatactivated free radical initiator. Typical thermal initiators includeperoxides such as benzoyl peroxide and azo compounds such asazobisisobutyronitrile, as well as dicumyl peroxide, which is favoredfor mill blanks.

In favored embodiments, such as when the dental composition is employedas a dental restorative (e.g. dental filling or crown) or an orthodonticcement, the dental composition typically comprises appreciable amountsof (e.g. nanoparticle) filler. Such compositions preferably include atleast 40 wt-%, more preferably at least 45 wt-%, and most preferably atleast 50 wt-% filler, based on the total weight of the composition. Insome embodiments the total amount of filler is at most 90 wt-%,preferably at most 80 wt-%, and more preferably at most 75 wt-% filler.

The (e.g. filled) dental composite materials typically exhibit adiametral tensile strength (DTS) of at least about 70, 75, or 80 MPaand/or a Barcol Hardness of at least about 60, or 65, or 70, or 75. Thedepth of cure ranges from about 4 to about 5 and comparable tocommercially available (e.g. filled) dental compositions suitable forrestorations.

In some embodiments, the compressive strength is at least 300, 325, 350or 375 MPa.

In some embodiments, such as compositions further comprising at leastone ethylenically unsaturated monomer with acid functionality, theadhesion to enamel and/or dentin is at least 5, 6, 7, 8, 9, or 10 MPa.

Dental compositions suitable for use as dental adhesives can optionallyalso include filler in an amount of at least 1 wt-%, 2 wt-%, 3 wt-%, 4wt-%, or 5 wt-% based on the total weight of the composition. For suchembodiments, the total concentration of filler is at most 40 wt-%,preferably at most 20 wt-%, and more preferably at most 15 wt-% filler,based on the total weight of the composition.

Fillers may be selected from one or more of a wide variety of materialssuitable for incorporation in compositions used for dental applications,such as fillers currently used in dental restorative compositions, andthe like.

The filler can be an inorganic material. It can also be a crosslinkedorganic material that is insoluble in the polymerizable resin, and isoptionally filled with inorganic filler. The filler is generallynon-toxic and suitable for use in the mouth. The filler can beradiopaque, radiolucent, or nonradiopaque. Fillers as used in dentalapplications are typically ceramic in nature.

Non-acid-reactive inorganic filler particles include quartz (i.e.,silica), submicron silica, zirconia, submicron zirconia, andnon-vitreous microparticles of the type described in U.S. Pat. No.4,503,169 (Randklev).

The filler can also be an acid-reactive filler. Suitable acid-reactivefillers include metal oxides, glasses, and metal salts. Typical metaloxides include barium oxide, calcium oxide, magnesium oxide, and zincoxide. Typical glasses include borate glasses, phosphate glasses, andfluoroaluminosilicate (“FAS”) glasses. The FAS glass typically containssufficient elutable cations so that a hardened dental composition willform when the glass is mixed with the components of the hardenablecomposition. The glass also typically contains sufficient elutablefluoride ions so that the hardened composition will have cariostaticproperties. The glass can be made from a melt containing fluoride,alumina, and other glass-forming ingredients using techniques familiarto those skilled in the FAS glassmaking art. The FAS glass typically isin the form of particles that are sufficiently finely divided so thatthey can conveniently be mixed with the other cement components and willperform well when the resulting mixture is used in the mouth.

Generally, the average particle size (typically, diameter) for the FASglass is no greater than 12 micrometers, typically no greater than 10micrometers, and more typically no greater than 5 micrometers asmeasured using, for example, a sedimentation particle size analyzer.Suitable FAS glasses will be familiar to those skilled in the art, andare available from a wide variety of commercial sources, and many arefound in currently available glass ionomer cements such as thosecommercially available under the trade designations VITREMER, VITREBOND,RELY X LUTING CEMENT, RELY X LUTING PLUS CEMENT, PHOTAC-FIL QUICK,KETAC-MOLAR, and KETAC-FIL PLUS (3M ESPE Dental Products, St. Paul,Minn.), FUJI II LC and FUJI IX (G-C Dental Industrial Corp., Tokyo,Japan) and CHEMFIL Superior (Dentsply International, York, Pa.).Mixtures of fillers can be used if desired.

Other suitable fillers are disclosed in U.S. Pat. No. 6,387,981 (Zhanget al.) and U.S. Pat. No. 6,572,693 (Wu et al.) as well as PCTInternational Publication Nos. WO 01/30305 (Zhang et al.), U.S. Pat. No.6,730,156 (Windisch et al.), WO 01/30307 (Zhang et al.), and WO03/063804 (Wu et al.). Filler components described in these referencesinclude nanosized silica particles, nanosized metal oxide particles, andcombinations thereof. Nanofillers are also described in U.S. Pat. No.7,090,721 (Craig et al.), U.S. Pat. No. 7,090,722 (Budd et al.) and U.S.Pat. No. 7,156,911; and U.S. Pat. No. 7,649,029 (Kolb et al.).

Examples of suitable organic filler particles include filled or unfilledpulverized polycarbonates, polyepoxides, poly(meth)acrylates and thelike. Commonly employed dental filler particles are quartz, submicronsilica, and non-vitreous microparticles of the type described in U.S.Pat. No. 4,503,169 (Randklev).

Mixtures of these fillers can also be used, as well as combinationfillers made from organic and inorganic materials.

Fillers may be either particulate or fibrous in nature. Particulatefillers may generally be defined as having a length to width ratio, oraspect ratio, of 20:1 or less, and more commonly 10:1 or less. Fiberscan be defined as having aspect ratios greater than 20:1, or morecommonly greater than 100:1. The shape of the particles can vary,ranging from spherical to ellipsoidal, or more planar such as flakes ordiscs. The macroscopic properties can be highly dependent on the shapeof the filler particles, in particular the uniformity of the shape.

Micron-size particles are very effective for improving post-cure wearproperties. In contrast, nanoscopic fillers are commonly used asviscosity and thixotropy modifiers. Due to their small size, highsurface area, and associated hydrogen bonding, these materials are knownto assemble into aggregated networks.

In some embodiments, the dental composition preferably comprise ananoscopic particulate filler (i.e., a filler that comprisesnanoparticles) having an average primary particle size of less thanabout 0.100 micrometers (i.e., microns), and more preferably less than0.075 microns. As used herein, the term “primary particle size” refersto the size of a non-associated single particle. The average primaryparticle size can be determined by cutting a thin sample of hardeneddental composition and measuring the particle diameter of about 50-100particles using a transmission electron micrograph at a magnification of300,000 and calculating the average. The filler can have a unimodal orpolymodal (e.g., bimodal) particle size distribution. The nanoscopicparticulate material typically has an average primary particle size ofat least about 2 nanometers (nm), and preferably at least about 7 nm.Preferably, the nanoscopic particulate material has an average primaryparticle size of no greater than about 50 nm, and more preferably nogreater than about 20 nm in size. The average surface area of such afiller is preferably at least about 20 square meters per gram (m²/g),more preferably, at least about 50 m²/g, and most preferably, at leastabout 100 m²/g.

In some preferred embodiments, the dental composition comprises silicananoparticles. Suitable nano-sized silicas are commercially availablefrom Nalco Chemical Co. (Naperville, Ill.) under the product designationNALCO COLLOIDAL SILICAS. For example, preferred silica particles can beobtained from using NALCO products 1040, 1042, 1050, 1060, 2327 and2329.

Silica particles are preferably made from an aqueous colloidaldispersion of silica (i.e., a sol or aquasol). The colloidal silica istypically in the concentration of about 1 to 50 weight percent in thesilica sol. Colloidal silica sols that can be used are availablecommercially having different colloid sizes, see Surface & ColloidScience, Vol. 6, ed. Matijevic, E., Wiley Interscience, 1973. Preferredsilica sols for use making the fillers are supplied as a dispersion ofamorphous silica in an aqueous medium (such as the Nalco colloidalsilicas made by Nalco Chemical Company) and those which are low insodium concentration and can be acidified by admixture with a suitableacid (e.g. Ludox colloidal silica made by E. I. Dupont de Nemours & Co.or Nalco 2326 from Nalco Chemical Co.).

Preferably, the silica particles in the sol have an average particlediameter of about 5-100 nm, more preferably 10-50 nm, and mostpreferably 12-40 nm. A particularly preferred silica sol is NALCO 1041.

In some embodiments, the dental composition comprises zirconiananoparticles. Suitable nano-sized zirconia nanoparticles can beprepared using hydrothermal technology as described in U.S. Pat. No.7,241,437 (Davidson et al.).

In some embodiments, lower refractive index (e.g. silica) nanoparticlesare employed in combination with high refractive index (e.g. zirconia)nanoparticles in order to index match (refractive index within 0.02) thefiller to the refractive index of the polymerizable resin.

In some embodiments, the nanoparticles are in the form of nanoclusters,i.e. a group of two or more particles associated by relatively weakintermolecular forces that cause the particles to clump together, evenwhen dispersed in a hardenable resin.

Preferred nanoclusters can comprise a substantially amorphous cluster ofnon-heavy (e.g. silica) particles, and amorphous heavy metal oxide (i.e.having an atomic number greater than 28) particles such as zirconia. Theparticles of the nanocluster preferably have an average diameter of lessthan about 100 nm. Suitable nanocluster fillers are described in U.S.Pat. No. 6,730,156 (Windisch et al.); incorporated herein by reference.

In some preferred embodiments, the dental composition comprisesnanoparticles and/or nanoclusters surface treated with an organometalliccoupling agent to enhance the bond between the filler and the resin. Theorganometallic coupling agent may be functionalized with reactive curinggroups, such as acrylates, methacrylates, vinyl groups and the like.

Suitable copolymerizable organometallic compounds may have the generalformulas: CH₂═C(CH₃)_(m)Si(OR)_(n) or CH₂═C(CH₃)_(m)C═OOASi(OR)_(n);wherein m is 0 or 1, R is an alkyl group having 1 to 4 carbon atoms, Ais a divalent organic linking group, and n is from 1 to 3. Preferredcoupling agents include gamma-methacryloxypropyltrimethoxysilane,gamma-mercaptopropyltriethoxysilane, gamma-aminopropyltrimethoxysilane,and the like.

In some embodiments, a combination of surface modifying agents can beuseful, wherein at least one of the agents has a functional groupco-polymerizable with a hardenable resin. Other surface modifying agentswhich do not generally react with hardenable resins can be included toenhance dispersibility or rheological properties. Examples of silanes ofthis type include, for example, aryl polyethers, alkyl, hydroxy alkyl,hydroxy aryl, or amino alkyl functional silanes.

The surface modification can be done either subsequent to mixing withthe monomers or after mixing. It is typically preferred to combine theorganosilane surface treatment compounds with nanoparticles beforeincorporation into the resin. The required amount of surface modifier isdependant upon several factors such as particle size, particle type,modifier molecular wt, and modifier type. In general it is preferredthat approximately a monolayer of modifier is attached to the surface ofthe particle.

The surface modified nanoparticles can be substantially fully condensed.Fully condensed nanoparticles (with the exception of silica) typicallyhave a degree of crystallinity (measured as isolated metal oxideparticles) greater than 55%, preferably greater than 60%, and morepreferably greater than 70%. For example, the degree of crystallinitycan range up to about 86% or greater. The degree of crystallinity can bedetermined by X-ray diffraction techniques. Condensed crystalline (e.g.zirconia) nanoparticles have a high refractive index whereas amorphousnanoparticles typically have a lower refractive index.

In some embodiments, the dental compositions can have an initial colorremarkably different than the cured dental structures. Color can beimparted to the composition through the use of a photobleachable orthermochromic dye. As used herein, “photobleachable” refers to loss ofcolor upon exposure to actinic radiation. The composition can include atleast 0.001 wt-% photobleachable or thermochromic dye, and typically atleast 0.002 wt-% photobleachable or thermochromic dye, based on thetotal weight of the composition. The composition typically includes atmost 1 wt-% photobleachable or thermochromic dye, and more typically atmost 0.1 wt-% photobleachable or thermochromic dye, based on the totalweight of the composition. The amount of photobleachable and/orthermochromic dye may vary depending on its extinction coefficient, theability of the human eye to discern the initial color, and the desiredcolor change. Suitable thermochromic dyes are disclosed, for example, inU.S. Pat. No. 6,670,436 (Burgath et al.).

For embodiments including a photobleachable dye, the color formation andbleaching characteristics of the photobleachable dye varies depending ona variety of factors including, for example, acid strength, dielectricconstant, polarity, amount of oxygen, and moisture content in theatmosphere. However, the bleaching properties of the dye can be readilydetermined by irradiating the composition and evaluating the change incolor. The photobleachable dye is generally at least partially solublein a hardenable resin.

Photobleachable dyes include, for example, Rose Bengal, MethyleneViolet, Methylene Blue, Fluorescein, Eosin Yellow, Eosin Y, Ethyl Eosin,Eosin bluish, Eosin B, Erythrosin B, Erythrosin Yellowish Blend,Toluidine Blue, 4′,5′-Dibromofluorescein, and combinations thereof.

The color change can be initiated by actinic radiation such as providedby a dental curing light which emits visible or near infrared (IR) lightfor a sufficient amount of time. The mechanism that initiates the colorchange in the compositions may be separate from or substantiallysimultaneous with the hardening mechanism that hardens the resin. Forexample, a composition may harden when polymerization is initiatedchemically (e.g., redox initiation) or thermally, and the color changefrom an initial color to a final color may occur subsequent to thehardening process upon exposure to actinic radiation.

Optionally, compositions may contain solvents (e.g., alcohols (e.g.,propanol, ethanol), ketones (e.g., acetone, methyl ethyl ketone), esters(e.g., ethyl acetate), other nonaqueous solvents (e.g.,dimethylformamide, dimethylacetamide, dimethylsulfoxide,1-methyl-2-pyrrolidinone)), and water.

If desired, the compositions can contain additives such as indicators,dyes, pigments, inhibitors, accelerators, viscosity modifiers, wettingagents, buffering agents, radical and cationic stabilizers (for exampleBHT,), and other similar ingredients that will be apparent to thoseskilled in the art.

Additionally, medicaments or other therapeutic substances can beoptionally added to the dental compositions. Examples include, but arenot limited to, fluoride sources, whitening agents, anticaries agents(e.g., xylitol), calcium sources, phosphorus sources, remineralizingagents (e.g., calcium phosphate compounds), enzymes, breath fresheners,anesthetics, clotting agents, acid neutralizers, chemotherapeuticagents, immune response modifiers, thixotropes, polyols,anti-inflammatory agents, antimicrobial agents (in addition to theantimicrobial lipid component), antifungal agents, agents for treatingxerostomia, desensitizers, and the like, of the type often used indental compositions. Combinations of any of the above additives may alsobe employed. The selection and amount of any one such additive can beselected by one of skill in the art to accomplish the desired resultwithout undue experimentation.

The curable dental composition can be used to treat an oral surface suchas tooth, as known in the art. In some embodiments, the compositions canbe hardened by curing after applying the dental composition. Forexample, when the curable dental composition is used as a restorativesuch as a dental filling, the method generally comprises applying thecurable composition to an oral surface (e.g. cavity); and curing thecomposition. In some embodiments, a dental adhesive may be applied priorto application of the curable dental restoration material describedherein. Dental adhesives are also typically hardened by curingconcurrently with curing the highly filled dental restorationcomposition. The method of treating an oral surface may compriseproviding a dental article and adhering the dental article to an oral(e.g. tooth) surface.

In other embodiments, the compositions can be hardened (e.g.,polymerized) into dental articles prior to applying. For example, adental article such as a crown may be pre-formed from the hardenabledental composition described herein. Dental composite (e.g. crowns)articles can be made from the curable composition described herein bycasting the curable composition in contact with a mold and curing thecomposition. Alternatively, dental composite (e.g. crowns) article canbe made by first curing the composition forming a mill blank and thenmechanically milling the composition into the desired article.

Another method of treating a tooth surface comprises providing a dentalcomposition as described herein wherein the composition is in the formof a (partially hardened) hardenable, self-supporting, malleablestructure having a first semi-finished shape; placing the hardenabledental composition on a tooth surface in the mouth of a subject;customizing the shape of the hardenable dental composition; andhardening the hardenable dental composition. The customization can occurin the patient's mouth or on a model outside the patient mouth such asdescribed in U.S. Pat. No. 7,674,850 (Karim et al.); incorporated hereinby reference.

Objects and advantages are further illustrated by the followingexamples, but the particular materials and amounts thereof recited inthese examples, as well as other conditions and details, should not beconstrued to unduly limit this invention. Unless otherwise indicated,all parts and percentages are on a weight basis.

Addition-Fragmentation Monomer (AFM) Synthesis

General Procedures.

All reactions were performed in round-bottomed flasks or glass jars orvials using unpurified commercial reagents.

Materials.

Commercial reagents were used as received. Dichloromethane, ethylacetate, and toluene were obtained from EMD Chemicals Inc. (Gibbstown,N.J., USA). Glycidyl methacrylate, 4-(dimethylamino)pyridine,methacryloyl chloride, triphenyl phosphine,2,6-di-t-butyl-4-methylphenol, and dibutyltin dilaurate were obtainedfrom Alfa Aesar (Ward Hill, Mass., USA). 2-Isocyantoethyl methacrylate,1,2-epoxy-3-phenoxypropane, and 1,2-epoxydecane were obtained from TCIAmerica (Portland, Oreg., USA). Acryloyl chloride, triethyl amine, andtriphenyl antimony were obtained from Sigma Aldrich (St. Louis, Mo.,USA). 4-hydroxybutyl acrylate glycidylether was obtained from NipponKasei Chemical (Tokyo, Japan). Glycidyl acrylate was obtained fromPolysciences Inc. (Warringotn, Pa., USA). Methyl methacrylate oligomermixture was obtained according to the procedure detailed in Example 1 ofU.S. Pat. No. 4,547,323 (Carlson, G. M.).

Instrumentation.

Proton nuclear magnetic resonance (1H NMR) spectra and carbon nuclearmagnetic resonance (13C NMR) spectra were recorded on a 400 MHzspectrometer.

Distillation of Methyl Methacrylate Oligomer Mixture

Distillation was performed as described in Moad, C. L.; Moad, G.;Rizzardo, E.; and Thang, S. H. Macromolecules, 1996, 29, 7717-7726, withdetails as follows:

A 1 L round-bottomed flask equipped with a magnetic stir bar was chargedwith 500 g of methyl methacrylate oligomer mixture. The flask was fittedwith a Vigreux column, a condenser, a distribution adapter, and fourcollection flasks. With stirring, the distillation apparatus was placedunder reduced pressure (0.25 mm Hg). The oligomer mixture was stirredunder reduced pressure at room temperature until gas evolution (removalof methyl methacrylate monomer) had largely subsided. The distillationpot was then heated to reflux in an oil bath to distill the oligomermixture. The fractions isolated by this procedure are listed in Table 1

TABLE 1 Fractions from the Distillation of Methyl Methacrylate OligomerMixture Boiling Pressure point Fraction (mmHg) (° C.) Mass (g)Approximate Composition A 0.25 59 63.27 Dimer B 0.09 47 115.97 Dimer C0.10 60-87 25.40 dimer (~50-75%), oligomers (mainly trimer) D 0.10 8715.20 dimer (~5%), oligomers (mainly trimer) E 0.13 105  156.66oligomers (trimer and higher)Hydrolysis of Methyl Methacrylate Dimer

Hydrolysis of the dimer to Diacid 1 was performed as described inHutson, L.; Krstina, J.; Moad, G.; Morrow, G. R.; Postma, A.; Rizzardo,E.; and Thang, S. H. Macromolecules, 2004, 37, 4441-4452, with detailsas follows:

A 1 L, round-bottomed flask equipped with a magnetic stir bar wascharged with deionized water (240 mL) and potassium hydroxide (60.0 g,1007 mmol). The mixture was stirred until homogeneous. Methylmethacrylate dimer (75.0 g, 374.6 mmol) was added. The reaction wasequipped with a reflux condenser and was heated to 90° C. in an oilbath. After 17 hours, the reaction was removed from the oil bath and wasallowed to cool to room temperature. The reaction solution was acidifiedto pH of approximately 1 using concentrated HCl. A white precipitateformed upon acidification. The heterogeneous mixture was vacuum filteredand quickly washed twice with 50-100 mL of deionized water. The whitesolid was dried by pulling air through the solid for approximately 4hours. The white solid was then dissolved in approximately 1750 mL ofdichloromethane. Only a very small amount (less than a gram) of solidremained insoluble. The solution was allowed to stand for 24 hours. Thedichloromethane solution was then vacuum filtered to remove theundissolved white solid. The filtered dichloromethane solution wasconcentrated in vacuo to provide a white solid. The solid was furtherdried under high vacuum to provide diacid 1 (55.95 g, 325.0 mmol, 87%)as a white powder.

Preparation of AFM-1

An approximately 250 mL amber bottle equipped with a magnetic stir barwas charged with glycidyl methacrylate (23.0 mL, 24.8 g, 174 mmol) andtriphenyl antimony (0.369 g, 1.04 mmol). The reaction was covered with aplastic cap with two 16 gauge needles pierced through the cap to allowair into the reaction. With stirring, the mixture was heated to 100° C.in an oil bath. Diacid 1 (15.0 g, 87.1 mmol) was added to the reactionin small portions over a period of 1.5 hours. After 21 hours, triphenylphosphine (0.091 g, 0.35 mmol) was added. The reaction was kept stirringat 100° C. After an additional 6.5 hours the reaction was sampled, and1H NMR analysis was consistent with the desired product as a mixture ofisomers and indicated consumption of glycidyl methacrylate. The reactionwas cooled to room temperature to provide AFM-1 as a clear, very paleyellow viscous material.

Preparation of AFM-2 via Diol 2

Preparation of Diol 2

An approximately 30 mL glass bottle equipped with a magnetic stir barwas charged with 1,2-epoxy-3-phenoxypropane (3.93 mL, 4.36 g, 29.0 mmol)and triphenyl antimony (0.0593 g, 0.168 mmol). The reaction was sealedwith a plastic cap. With stirring, the mixture was heated to 100° C. inan oil bath. Diacid 1 (2.50 g, 14.5 mmol) was added to the reaction insmall portions over a period of 35 minutes. After 18 hours, triphenylphosphine (0.0162 g, 0.0618 mmol) was added. The reaction was keptstirring at 100° C. After an additional 24 hours, the reaction wassampled and 1H NMR analysis was consistent with the desired product as amixture of isomers. The reaction was cooled to room temperature toprovide diol 2 as a clear, colorless glassy material.

Preparation of AFM-2

A 100 mL round-bottomed flask equipped with a magnetic stir bar wascharged with diol 2 (4.956 g, 10.49 mmol) and dichloromethane (20 mL).With stirring, 2-isocyanatoethyl methacrylate (2.20 mL, 2.416 g, 20.98mmol) was added. Dibutyltin dilaurate (3 drops from a glass pipette) wasadded to the clear and homogeneous solution. The reaction was sealedwith a plastic cap with a 16 gauge needle added to vent to air. After 72hours, the reaction mixture was concentrated in vacuo to a clear viscousliquid. The liquid was transferred to a 25 mL amber bottle using a smallamount of dichloromethane. Air was bubbled through the viscous materialto remove solvent. 1H NMR analysis was consistent with the desiredproduct as a mixture of isomers. AFM-2 (7.522 g, 9.63 mmol, 92%) wasobtained as a very viscous, clear oil.

Preparation of AFM-3

A two-neck, 500 mL round-bottomed flask equipped with a magnetic stirbar was charged with AFM-1 (20.00 g, 43.81 mmol) and dichloromethane(160 mL). The necks on the reaction flask were sealed with plastic capsand a 16 gauge needle was added to each cap to vent the reaction to air.The reaction was cooled to 0° C. with stirring. Triethylamine (30.5 mL,22.1 g, 219 mmol) and 4-(dimethylamino)pyridine (1.609 g, 13.17 mmol)were added. Methacryloyl chloride (17.0 ml, 18.4 g, 176 mmol) was addedto the reaction mixture dropwise over a period of 40 minutes. The paleyellow, heterogeneous reaction was allowed to slowly warm to roomtemperature. After 24 hours, the pale yellow reaction solution wasconcentrated in vacuo. Ethyl acetate (400 mL) was added to the residueand the mixture was transferred to a 1 L separatory funnel. The reactionflask was washed with aqueous hydrochloric acid (1N, 200 mL) and theaqueous hydrochloric acid solution was added to the separatory funnel.The solutions were mixed well and the aqueous layer was removed. Theorganic solution was further washed twice with 200 mL aqueoushydrochloric acid (1N), once with 200 mL of deionized water, three timeswith 200 mL of aqueous sodium hydroxide (1N), and once with 200 mL of asaturated aqueous solution of sodium chloride. The organic solution wasdried over sodium sulfate for 30 minutes and then filtered.2,6-di-t-butyl-4-methylphenol (0.011 g) was added, and the solution wasconcentrated in vacuo (bath temperature less than 20° C.) to a viscoussolution. The concentrated solution was transferred to an amber bottleusing a small amount of dichloromethane to ensure quantitative transfer.Air was bubbled through the viscous material to remove solvent. 1H NMRanalysis was consistent with the desired product as a mixture ofisomers. AFM-3 (23.44 g, 39.55 mmol, 90%) was obtained as a veryviscous, very pale yellow oil.

Preparation of AFM-4

A three-neck, 250 mL round-bottomed flask was equipped with a magneticstir bar. Diol 2 (6.86 g, 14.52 mmol) was dissolved in dichloromethane(25 mL) and added to the reaction flask. Five additional 5 mL portionsof dichloromethane were used to ensure quantitative transfer of diol 2and these rinses were added to the reaction flask. The reaction flaskwas equipped with a pressure-equalizing addition funnel capped with aplastic cap. The other two necks on the reaction flask were also sealedwith plastic caps, and a 16 gauge needle was added to each to vent thereaction to air. The reaction was cooled to 0° C. with stirring.Triethylamine (10.0 mL, 7.26 g, 71.8 mmol) and 4-(dimethylamino)pyridine(0.532 g, 4.36 mmol) were added. A 37.3 wt. % solution of methacryloylchloride in toluene (16.28 g solution, 6.07 g methacryloyl chloride,58.1 mmol) was added to the addition funnel. The toluene solution ofmethacryloyl chloride was added to the reaction mixture dropwise over aperiod of 30 minutes. The reaction became pale yellow. After 18 hours,the pale yellow reaction solution was transferred to a 500 mL separatoryfunnel using dichloromethane (200 mL). The organic solution was washedtwice with 150 mL of aqueous hydrochloric acid (1N), once with 150 mL ofdeionized water, twice with 150 mL of aqueous sodium hydroxide (1N), andonce with 200 mL of a saturated aqueous solution of sodium chloride. Theorganic solution was dried over sodium sulfate for 30 minutes, and wasthen filtered and concentrated in vacuo (bath temperature less than 20°C.) to a viscous solution. The concentrated solution was transferred toan amber bottle using a small amount of dichloromethane to ensurequantitative transfer. Air was bubbled through the viscous material toremove solvent. 1H NMR analysis was consistent with the desired productas a mixture of isomers. AFM-4 (8.463 g, 13.9 mmol, 96%) was obtained asa very viscous, pale yellow oil.

BisGMA (2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane(Sigma Aldrich, St. Louis, Mo.)

TEGDMA (triethyleneglycol dimethacrylate, Sartomer Co., Inc., Exton,Pa.)

UDMA (Diurethane dimethacrylate, CAS No. 41137-60-4, commerciallyavailable as Rohamere 6661-0, Rohm Tech, Inc., Malden, Mass.)

BisEMA6 (ethoxylated bisphenol A methacrylate as further described inU.S. Pat. No. 6,030,606, available from Sartomer as “CD541”)

Procrylat (2,2-Bis-4-(3-hydroxy-propoxy-phenyl)propane dimethacrylate,CAS 27689-2-9, prepared as described in WO 2006/020760)

CAPA2125 IEM (refers to the reaction product of CAPA2125 (apolycaprolactone polyol available from Solvay Chemical Company,Warrington, UK) and two equivalents of 2-isocyanatoethyl methacrylate,prepared essentially as described in U.S. Pat. No. 6,506,816)

GDMA-P (75 wt % glycerol dimethacrylate phosphate (prepared as describedin J. Dent. Res., 35, 8466 (1956), may also be prepared as described inExample 2 of U.S. Pat. No. 6,187,838) mixed with 25% wt % TEGDMA)

CPQ (camphorquinone, Sigma Aldrich, St. Louis, Mo.)

EDMAB (ethyl 4-(N,N-dimethylamino)benzoate, Sigma Aldrich)

DPIHFP (diphenyl iodonium hexafluorophosphate, Alpha Aesar, Ward Hill,Mass.)

BHT (butylated hydroxytoluene, Sigma Aldrich)

BZT (refers to 2-(2-hydroxy-5-methacryloxyethylphenyl)-2H-benzotriazole,Ciba, Inc., Tarrytown, N.Y.)

HEMA (2-hydroxyethyl methacrylate, Sigma-Aldrich)

Tris-(2-hydroxyethyl)isocyanurate (TCI America, Portland, Oreg.)

DCC (dicyclohexyl carbodimide, TCI)

YbF₃ (ytterbium fluoride, Treibacher, Germany)

MEHQ (hydroquinone monomethyl ether, Sigma-Aldrich)

“Irgacure 819” (phosphine oxide photoinitiator, available from CibaSpecialty Chemicals Corp., Tarrytown, N.Y.)

Zr/Si filler (surface treated, one hundred parts zirconia silica fillerof average particle size 0.6-0.9 micrometers was mixed with deionizedwater at a solution temperature of between 20-30° C., and the pH isadjusted to 3-3.3 with trifluoroacetic acid (0.278 parts). A-174 silane(SILQUEST A-174, gamma.-methacryloxypropyltrimethoxysilane, CromptonCorporation, Naugatuck, Conn.) was added to the slurry in an amount 7parts and the blend is mixed over 2 hours. At the end of 2 hours, the pHis neutralized with calcium hydroxide. The filler is dried, crushed andscreened through a 74 or 100 micron screen.)Zr/Si Nano-Cluster Filler (silane-treated zirconia/silica nanoclusterfiller prepared essentially as described in U.S. Pat. No. 6,730,156(Preparatory Example A (line 51-64) and Example B (column 25 line 65through column 26 line 40))75 nm Silica filler (prepared as described for Filler A in Column 22 ofU.S. Pat. No. 7,393,882)20 nm Silica filler (silane-treated nano-sized silica having a nominalparticle size of approximately 20 nanometers, prepared essentially asdescribed in U.S. Pat. No. 6,572,693 B1, (column 21, lines 63-67 forNanosized particle filler, Type #2))Aerosil R812S (fumed silica, Degussa, Germany)Isocyanurate Trimer—Synthesis of Tri-HydroxyEthyl Iso Cyanurate TrisHEMA Phthalate

Phthalic acid anhydride (57.0 g, 0.385 mol, CAS #85-33-9, Alfa Aesar,lot G30T004), 4-(dimethylamino)pyridine (DMAP, 4.9 g, 0.04 mol, CAS#1122-58-3, Alfa Aesar, lot L125009), 2-hydroxyethylmethacrylate (HEMA,50.9 g, 0.391 mol, and butylated hydroxytoluene (BHT, 0.140 g) werecharged into a 2-liter 3-neck reaction flask equipped with a mechanicalstirrer, a thermocouple connected to a temperature controller, a dry airstream running through a T-shape connection into the reactor then to anoil bubbler, and a heating mantle. With continuous stirring, the flaskcontents were heated to 95° C., by which all components dissolved and aclear liquid was obtained. Heating at 95° C. and stirring were continuedfor 5 hours. The heat was turned off and the flask contents were allowedto cool to room temperature while still being stirred under dry air.Acetone (250 ml) was added followed by tris-(2-hydroxyethyl)isocyanurate(33.58 g, 0.158 mol, from TCI). The heating mantle was replaced with anice bath, where the mixture was cooled to 0-5° C. A solution made fromdicyclohexyl carbodiimide (DCC, 81 g, 0.393 mol) in 120 ml acetone wasplaced into a 500 ml dropping funnel which was placed in-between thereaction flask and the dry air in-let. The DCC solution was added slowlyto the continuously stirred reaction mixture in a rate where thereaction mixture temperature would not exceed 10° C. After completeaddition of the DCC solution, the reaction was stirred in the ice bathfor 2 hours in at room temperature overnight. On day 2, the solid formedwas removed by vacuum filtration and the residue was concentrated in arotary evaporator at 40-45° C. bath. The residue was dissolved in 300 mlsolution of ethylacetate:hexanes, 2:1 by volume. The obtained solutionwas extracted with 200 ml of 1.0 N. HCl, 200 ml of 10% aqueous, 200 mlH₂O, and 200 ml brine. The organic layer was concentrated in a rotaryevaporator with 40° C. bath. Further drying was done under a vacuum pumpat 50° C. for 3 hours with air bleeding into the product during thewhole time to give an almost colorless hazy viscous liquid.

Refractive index was measured and found to be 1.5386. By use of NMR theliquid was determined to be the product shown is the following reactionscheme. The calculated molecular weight of the depicted end product wasdetermined to be 1041 g/mole.

The calculated molecular weight of the linking group was determined tobe 220 g/mole.

Synthesis of TGP-IEMGeneral Procedure 1: Reaction of a Diol-Precursor with Epoxiy ComponentsUsing TEAA as Catalyst

E.g. TCD alcohol and GMA as the corresponding epoxy functional reagent/sare mixed while stirring with e.g. cyclohexane. 1.5 wt.-% of TEA and 1.5wt.-% of GAA (with respect to the mass of the sum of all reactants, toform in situ TEAA), 1000 ppm of HQ, 200 ppm of BHT, and 200 ppm of HQMEare added while stirring. Then the mixture is heated while stirring atemperature of about 70° C. until completion of the addition reaction(measured via ¹H-NMR: no signals of residual epoxy groups weredetected). Optionally, 3 to 5 wt.-% of MSA is slowly added whilestirring and stirring is continued for about 60 min at about 70° C. Thenthe mixture is allowed to cool to room temperature while stirring. Theupper cyclohexane phase is separated from the oily viscous lower phaseif existent. The separated cyclohexane phase is washed once with water,then extracted twice with 2N NaOH solution, then once washed with water,then dried over anhydrous Na₂SO₄. After filtration, the filtrate isagain filtered through basic alumina 100 ppm of BHT and 100 ppm of HQMEare added to the filtrate. Then the solvent is stripped off in vacuumwhile air is bubbling through the crude sample.

According to General Procedure 1 100 g of TCD alcohol, 155 g of GP, and3.00 g of MSA were reacted. 253 g of TGP (509 mmol, 99%) were isolatedas yellow oil. According to General Procedure 4 100 g of TGP and 59.4 gof IEM were reacted. 158 g of TGP-IEM (196 mmol, 99%) were isolated asyellow oil: η=1400 Pa*s, n_(D) ²⁰=1.531.

Synthesis of TTEO-IEM

General Procedure 2: Reaction of a Diol-Precursor Like with EpoxyComponents Containing Mixtures (e.g. EO in THF) Using BF₃*THF asCatalyst

E.g. TCD alcohol is diluted in anhydrous THF, then BF₃*THF is addedwhile stirring. Gaseous EO is added while stirring so that thetemperature of the reaction mixture does not exceed about 30-40° C.After completion of the EO addition stirring is continued at roomtemperature for about 30 min. 13 wt.-% of water (with respect to the sumof the amounts of the reactive educts) are added, after about 30 minwhile stirring 13 wt.-% of basic alumina is added, too. After additionalabout 60 min of stirring 13 wt.-% of a solution of sodium methanolate inmethanol (30% in methanol) is added. Then the suspension is stirred atroom temperature for about 12 h. After filtration the solvent isstripped off in vacuum.

According to General Procedure 2 300 g of TCD alcohol, 64.6 g of EO, 600g of THF, and 37.9 g of BF₃*THF were reacted. 429 g of TTEO wereisolated as colorless oil. According to General Procedure 4 55.3 g ofTTEO and 54.7 g of IEM were reacted. 100 g of TTEO-IEM (95%) wereisolated as colorless oil: η=45 Pa*s, n_(D) ²⁰=1.503.

Synthesis of TTEO-MA:

General Procedure 3: Reaction of a Diol-Precuror Like e.g. TCD alcoholwith Epoxy Containing Mixtures (e.g. EO in THF) Using BF₃*THF asCatalyst

E.g. TCD alcohol is diluted in anhydrous THF, then BF₃*THF is addedwhile stirring. Gaseous EO is added while stirring so that thetemperature of the reaction mixture does not exceed about 30-40° C.After completion of the EO addition stirring is continued at roomtemperature for about 30 min. 13 wt.-% of water (with respect to the sumof the amounts of the reactive educts) are added, after about 30 minwhile stirring 13 wt.-% of basic alumina is added, too. After additionalabout 60 min of stirring 13 wt.-% of a solution of sodium methanolate inmethanol (30% in methanol) is added. Then the suspension is stirred atroom temperature for about 12 h. After filtration the solvent isstripped off in vacuum.

According to General Procedure 3 300 g of TCD alcohol, 64.6 g of EO, 600g of THF, and 37.9 g of BF₃*THF were reacted. 429 g of TTEO wereisolated as colorless oil. According to General Procedure 4 213 g ofTTEO, 161 g of MA, 44.8 mg of BHT, 121 mg of HQME, 89.6 mg of methyleneblue, and 12.8 g of MSA were reacted using hexane as solvent. 237 g ofTTEO-MA (67%) were isolated as colorless liquid: η=0.1 Pa*s, n_(D)²⁰=1.499.

Test Methods

Stress Test Method

To measure stress development during the curing process, a slot wasmachined into a rectangular 15×8×8 mm aluminum block, as shown inFIG. 1. The slot was 8 mm long, 2.5 mm deep, and 2 mm across, and waslocated 2 mm from an edge, thus forming a 2 mm wide aluminum cuspadjacent to a 2 mm wide cavity containing dental compositions beingtested. A linear variable displacement transducer (Model GT 1000, usedwith an E309 analog amplifier, both from RDP Electronics, UnitedKingdom) was positioned as shown to measure the displacement of the cusptip as the dental composition photocured at room temperature. Prior totesting, the slot in the aluminum block was sandblasted using RocatecPlus Special Surface Coating Blasting Material (3M ESPE), treated withRelyX Ceramic Primer (3M ESPE), and finally treated with a dentaladhesive, Adper Easy Bond (3M ESPE).

The slot was fully packed with the mixtures shown in the tables, whichequalled approximately 100 mg of material. The material was irradiatedfor 1 minute with a dental curing lamp (Elipar S-10, 3M ESPE) positionedalmost in contact (<1 mm) with the material in the slot, then thedisplacement of the cusp in microns was recorded 9 minutes after thelamp was extinguished.

Watts Shrinkage Test Method

The Watts Shrinkage (Watts) Test Method measures shrinkage of a testsample in terms of volumetric change after curing. The samplepreparation (90-mg uncured composite test sample) and test procedurewere carried out as described in the following reference: Determinationof Polymerization Shrinkage Kinetics in Visible-Light-Cured Materials:Methods Development, Dental Materials, October 1991, pages 281-286. Theresults are reported as negative % shrinkage.

Diametral Tensile Strength (DTS) Test Method

Diametral tensile strength of a test sample was measured according tothe following procedure. An uncured composite sample was injected into a4-mm (inside diameter) glass tube; the tube was capped with siliconerubber plugs. The tube was compressed axially at approximately 2.88kg/cm² pressure for 5 minutes. The sample was then light cured for 80seconds by exposure to a XL 1500 dental curing light (3M Company, St.Paul, Minn.), followed by irradiation for 90 seconds in a Kulzer UniXScuring box (Heraeus Kulzer GmbH, Germany) Cured samples were allowed tostand for 1 hour at about 37° C./90%+Relative Humidity. The sample wascut with a diamond saw to form disks about 2.2 mm thick, which werestored in distilled water at 37° C. for about 24 hours prior to testing.Measurements were carried out on an Instron tester (Instron 4505,Instron Corp., Canton, Mass.) with a 10 kilonewton (kN) load cell at acrosshead speed of 1 mm/minute according to ISO Specification 7489 (orAmerican Dental Association (ADA) Specification No. 27). Six disks ofcured samples were prepared and measured with results reported in MPa asthe average of the six measurements.

Barcol Hardness Test Method

Barcol Hardness of a test sample was determined according to thefollowing procedure. An uncured composite sample was cured in a 2.5-mmor 4-mm thick TEFLON mold sandwiched between a sheet of polyester (PET)film and a glass slide for 20 seconds and cured with an ELIPAR Freelight2 dental curing light (3M Company). After irradiation, the PET film wasremoved and the hardness of the sample at both the top and the bottom ofthe mold was measured using a Barber-Coleman Impressor (a hand-heldportable hardness tester; Model GYZJ 934-1; Barber-Coleman Company,Industrial Instruments Division, Lovas Park, Ind.) equipped with anindenter. Top and bottom Barcol Hardness values were measured at 5minutes after light exposure.

Depth of Cure Test Method

The depth of cure was determined by filling a 10 millimeter stainlesssteel mold cavity with the composite, covering the top and bottom of themold with sheets of polyester film, pressing the sheets to provide aleveled composition surface, placing the filled mold on a whitebackground surface, irradiating the dental composition for 20 secondsusing a dental curing light (3M Dental Products Curing Light 2500 or 3MESPE Elipar FreeLight2, 3M ESPE Dental Products), separating thepolyester films from each side of the mold, gently removing (byscraping) materials from the bottom of the sample (i.e., the side thatwas not irradiated with the dental curing light), and measuring thethickness of the remaining material in the mold. The reported depths arethe actual cured thickness in millimeters divided by 2.

Flexural Strength and Flexural Modulus Test Method

A paste sample was extruded into a 2 mm×2 mm×25 mm quartz glass moldforming a test bar. The material was then cured through the mold using 2standard dental cure lights (3M ESPE XL2500 or 3M ESPE XL3000). Thesamples were cured by placing one light in the center of the sample bar,curing for 20 sec, then simultaneously curing the ends of the bar for 20sec, flipping and repeating.

The samples were stored submerged in distilled water at 37 deg. C. priorto testing (16 to 24 hrs). Flexural Strength and Flexural Modulus of thebars was measured on an Instron tester (Instron 4505 or Instron 1123,Instron Corp., Canton, Mass.) according to ANSI/ADA (American NationalStandard/American Dental Association) specification No. 27 (1993) at acrosshead speed of 0.75 mm/minute. The results were reported inmegapascals (MPa).

Compressive Strength Test Method

Compressive strength of a test sample was measured according to thefollowing procedure. An uncured composite sample was injected into a4-mm (inside diameter) glass tube; the tube was capped with siliconerubber plugs; and then the tube was compressed axially at approximately2.88 kg/cm² pressure for 5 minutes. The sample was then light cured for80 seconds by exposure to a XL 1500 dental curing light (3M Company, St.Paul, Minn.), followed by irradiation for 90 seconds in a Kulzer UniXScuring box (Heraeus Kulzer GmbH, Germany) Cured samples were allowed tostand for 1 hour at about 37° C./90%+Relative Humidity and then were cutwith a diamond saw to form 8-mm long cylindrical plugs for measurementof compressive strength. The plugs were stored in distilled water at 37°C. for about 24 hours prior to testing. Measurements were carried out onan Instron tester (Instron 4505, Instron Corp., Canton, Mass.) with a 10kilonewton (kN) load cell at a crosshead speed of 1 mm/minute accordingto ISO Specification 7489 (or American Dental Association (ADA)Specification No. 27). Five cylinders of cured samples were prepared andmeasured with the results reported in MPa as the average of the fivemeasurements.

Adhesion Shear Bond Strength to Enamel or Dentin Test Method

Preparation of Teeth: Bovine incise teeth, free of soft tissue, wereembedded in circular acrylic disks. The embedded teeth were stored inwater in a refrigerator prior to use. In preparation for adhesivetesting, the embedded teeth were ground to expose a flat enamel ordentin surface using 120-grit sandpaper mounted on a lapidary wheel.Further grinding and polishing of the tooth surface was done using320-grit sandpaper on the lapidary wheel. The teeth were continuouslyrinsed with water during the grinding process. The polished teeth werestored in deionized water and used for testing within 2 hours afterpolishing. The teeth were allowed to warm in a 36 deg. C. oven tobetween room temperature (23 deg. C.) and 36 deg. C. before use.

Teeth Treatment: A reinforcement label (having an opening 150 micronsthick and 5 mm in diameter) was applied to the prepared tooth surfacesand a thin layer of the composite was applied with a dental applicatorbrush within the label opening, brushing for 20 sec. The composite layerwas cured for 20 sec. using an Elipar S10 curing light (3M ESPE). Next,a teflon mold having an opening (2 mm thick by 5 mm diameter) was placedover the cured layer of composite, filled with more of the samecomposite, and the composite was cured for 20 sec. using the S10 curinglight. This formed a button of cured composite adhered to the preparedtooth surface.

Adhesive Bond Strength Testing: The adhesive strength of a cured testexample was evaluated by mounting the assembly (described above) in aholder clamped in the jaws of an INSTRON testing machine (Instron 4505,Instron Corp. Canton, Mass.) with the polished tooth surface orientedparallel to the direction of pull. A loop of orthodontic wire (0.44-mmdiameter) was placed around the composite button adjacent to thepolished tooth surface. The ends of the orthodontic wire were clamped inthe pulling jaw of the INSTRON apparatus and pulled at a crosshead speedof 2 mm/min, thereby placing the adhesive bond in shear stress. Theforce in kilograms (kg) at which the bond failed was recorded, and thisnumber was converted to a force per unit area (units of kg/cm² or MPa)using the known surface area of the button. Each reported value ofadhesion to enamel or adhesion to dentin represents the average of 4 to5 replicates.

Paste Compositions

The components shown in the tables were measured and mixed togetheruntil uniform.

TTEO- Isocyanurate TTEO- Zr/Si AFM wt % IEM Trimer MA CPQ EDMAB DPIHFPFiller AFM-1 AFM-2 of resin only CE1 9.599 9.655 1.951 0.037 0.209 0.10878.44 1 9.547 9.54 1.915 0.035 0.211 0.106 78.43 0.21 0.99 2 9.422 9.3831.89 0.039 0.207 0.104 78.42 0.54 2.48 3 9.161 9.204 1.817 0.032 0.2030.101 78.42 1.06 4.91 4 8.947 8.921 1.789 0.032 0.196 0.101 78.42 1.597.371 CE2 9.995 10.162 1.055 0.032 0.216 0.11 78.43 5 9.922 10.052 1.0340.037 0.214 0.106 78.42 0.21 0.99 6 9.777 9.9 1.003 0.037 0.207 0.10678.44 0.53 2.46 7 9.517 9.622 1.022 0.032 0.203 0.101 78.43 1.07 4.97 89.269 9.383 0.989 0.037 0.198 0.099 78.43 1.6 7.409 TTEO- IsocyanurateTTEO- Zr/Si AFM wt % IEM Trimer MA CPQ EDMAB DPIHFP Filler AFM-3 AFM-4of resin only CE3 9.925 10.063 1.039 0.032 0.181 0.092 78.67  9 9.8229.959 1.028 0.032 0.179 0.09 78.68 0.21 0.98 10 9.659 9.796 1.011 0.030.177 0.087 78.71 0.53 2.48 11 9.425 9.558 0.987 0.03 0.173 0.085 78.691.05 4.93 12 9.195 9.323 0.962 0.03 0.169 0.083 78.66 1.58 7.39 CE49.907 10.043 1.055 0.036 0.209 0.109 78.64 13 9.806 9.943 1.045 0.0380.211 0.105 78.64 0.21 0.98 14 9.661 9.794 1.027 0.038 0.205 0.109 78.640.52 2.45 15 9.409 9.539 1.002 0.038 0.216 0.105 78.64 1.05 4.92 169.166 9.292 0.976 0.034 0.209 0.107 78.64 1.58 7.38 TGP- IsocyanurateTTEO- Zr/Si AFM wt % IEM Trimer MA CPQ EDMAB DPIHFP Filler AFM-1 ofresin only CE5 9.6 9.655 1.951 0.037 0.209 0.108 78.44 17 9.55 9.541.915 0.035 0.211 0.106 78.43 0.21 0.99 18 9.42 9.383 1.89 0.039 0.2070.104 78.42 0.54 2.48 19 9.16 9.204 1.817 0.032 0.203 0.101 78.42 1.064.91 20 8.95 8.921 1.789 0.032 0.196 0.101 78.42 1.59 7.371

The test results are reported as follows. For each test the average isreported followed by the standard deviation in parenthesis. The numberof samples utilized for each test is reported in the first row as “n”.Thus, n=3 means three samples were tested.

Barcol Barcol Watts Diametral Barcol hardness, Barcol hardness, Stress,um shrinkage, tensile hardness, 2.5 mm, hardness, 4.0 mm, Depthdeflection negative strength, 2.5 mm, bottom 4.0 mm, bottom of Cure, (n= 3) % (n = 5) MPa (n = 6) top (n = 6) (n = 6) top (n = 6) (n = 6) mm (n= 3) CE1 2.01 (0.11) 1.51 (0.04) 87.8 (5.2) 67.5 (2.5) 65.7 (2.1) 67.7(2.6) 72.8 (1.6) 5.04 (0.11)  1 1.57 (0.14) 1.50 (0.05) 81.6 (3.9) 66.3(1.4) 66.5 (2.6) 66.8 (1.3) 69.3 (1.2) 4.84 (0.22)  2 0.96 (0.04) 1.19(0.06) 84.0 (7.8) 40.5 (3.0) 49.7 (5.0) 50.7 (1.2) 53.5 (3.0) 4.43(0.04)  3 0.96 (0.02) 1.15 (0.01) 84.3 (3.0) 41.5 (3.3) 47.2 (3.0) 50.7(1.4) 49.7 (0.8) 4.29 (0.08)  4 0.77 (0.05) 1.15 (0.05) 85.4 (7.7) 43.5(5.8) 39.0 (5.9) 46.8 (1.5) 50.3 (3.4) 4.21 (0.07) CE2 2.02 (0.13) 1.42(0.04) 88.3 (2.1) 71.8 (0.8) 66.5 (1.8) 71.0 (1.1) 68.5 (0.8) 5.08(0.03)  5 1.76 (0.08) 1.31 (0.02) 89.2 (5.4) 66.2 (0.8) 67.3 (2.1) 69.3(0.8) 68.5 (2.4) 4.74 (0.09)  6 1.50 (0.11) 1.24 (0.05) 86.2 (3.2) 58.8(1.7) 64.0 (1.6) 64.5 (1.1) 65.3 (0.8) 4.58 (0.05)  7 0.86 (0.03) 1.08(0.04) 81.7 (5.3) 50.8 (1.5) 53.5 (2.1) 54.2 (1.8) 56.2 (2.3) 4.39(0.05)  8 0.54 (0.06) 0.98 (0.04) 79.2 (3.6) 29.0 (7.1) 36.3 (2.8) 41.2(1.5) 44.3 (2.4) 3.98 (0.11) CE3 1.78 (0.16) 1.39 (0.03)  87.9 (12.7)66.7 (1.8) 71.0 (1.6) 69.5 (1.9) 70.7 (1.2) 4.55 (0.14)  9 1.82 (0.12)1.35 (0.02) 85.9 (8.3) 64.7 (1.2) 66.2 (1.9) 66.0 (1.3) 69.5 (1.1) 4.50(0.06) 10 1.42 (0.17) 1.31 (0.04) 89.7 (6.7) 61.0 (2.1) 65.0 (0.9) 66.5(1.6) 68.3 (1.4) 4.35 (0.04) 11 1.16 (0.06) 1.21 (0.03) 87.6 (9.3) 54.5(2.4) 55.5 (1.9) 59.0 (2.6) 65.2 (1.5) 3.96 (0.10) 12 0.95 (0.04) 1.14(0.01)  85.2 (16.9) 49.0 (1.8) 54.8 (0.8) 54.3 (1.4) 55.2 (2.3) 3.80(0.10) CE4 1.71 (0.06) 1.36 (0.02) 76.9 (3.8) 64.2 (0.8) 69.7 (2.4) 65.3(1.2) 70.0 (1.3) 4.38 (0.06) 13 1.68 (0.01) 1.40 (0.07) 82.7 (6.5) 66.0(1.4) 69.3 (0.8) 65.5 (1.1) 68.7 (1.9) 4.37 (0.12) 14 1.44 (0.02) 1.35(0.01) 84.3 (3.8) 60.3 (1.5) 67.8 (1.0) 64.3 (1.0) 65.7 (1.2) 4.24(0.15) 15 0.98 (0.08) 1.24 (0.04) 84.1 (8.5) 54.8 (2.5) 58.5 (1.1) 56.3(2.7) 59.8 (1.2) 3.85 (0.00) 16 0.88 (0.03) 1.17 (0.02) 78.2 (6.0) 51.7(0.8) 54.3 (1.6) 49.7 (1.8) 55.3 (1.0) 3.66 (0.04) CE5 1.35 (0.17) 1.28(0.05) 78.5 (3.2) 65.3 (0.8) 69.5 (2.3) 66.5 (3.4) 61.3 (3.7) 4.70(0.05) 17 1.25 (0.15) 1.24 (0.06) 73.8 (6.5) 64.7 (1.6) 62.7 (2.0) 59.2(1.3) 62.7 (1.6) 4.62 (0.14) 18 1.10 (0.16) 1.17 (0.03) 74.0 (6.6) 57.7(1.6) 61.3 (1.2) 57.3 (2.2) 57.7 (2.0) 4.35 (0.07) 19 0.62 (0.08) 1.05(0.01) 78.0 (3.1) 51.8 (1.6) 51.2 (4.6) 53.7 (1.4) 49.0 (4.1) 4.19(0.03) 20 0.55 (0.09) 1.03 (0.02) 72.6 (6.8) 53.2 (2.1) 51.2 (1.7) 44.3(3.4) 39.2 (5.4) 4.10 (0.05)

The test results show the improved properties of Examples 1-20,comprising addition fragmentation materials, in comparison to CE1-CE5that lack the inclusion of an addition fragmentation material. Inparticular, as the concentration of addition fragmentation materials,increased the compositions exhibits reduced stress and reduced WattsShrinkage while maintaining sufficient Diametral tensile strength,Barcol hardness and depth of cure.

Dental compositions were also prepared wherein an addition-fragmentationmonomer was added to a conventional dental composition. Compositions CE6and 21 also contained 0.108 of DFIHFP and 0.03 of BHT.

Zr/Si Nano- AFM wt % BisGMA TEGDMA UDMA BisEMA6 CPQ EDMAB BZT AFM-1Cluster Filler of resin only CE6 5.161 1.175 7.226 7.226 0.04 0.215 0.3278.5 21 4.774 1.089 6.684 6.684 0.04 0.215 0.32 1.61 78.5 7.73

The test results are reported as follows. For each test the average isreported followed by the standard deviation in parenthesis. The numberof samples utilized for each test is reported in the first row as “n”.

Watts Diametral Barcol Barcol Stress, um shrinkage, tensile hardness,hardness, Depth of deflection negative % strength, 2.5 mm, top 2.5 mm,bottom Cure, (n = 2) (n = 5) MPa (n = 4-6) (n = 6) (n = 6) mm (n = 3)CE6 4.08 (0.18) 1.87 (0.04) 75.9 (3.0) 76.3 (1.4) 78.8 (1.5) 4.68 (0.10)21 2.91 (0.28) 1.77 (0.04) 71.2 (9.4) 76.0 (2.6) 73.7 (1.7) 4.24 (0.05)

Compositions CE7-26, as follows, also contained 0.06 CPQ, 0.108 ofDFIHFP, 0.216 EDMAB, 0.03 of BHT, 0.22 BZT, and 3.0 YbF3.

CAPA Zr/Si Nano- 75 nm 20 nm AFM wt % 2125 Zr/Si Cluster Silica Silicaof resin BisGMA TEGDMA Procrylat IEM AFM-1 Filler Filler filler filleronly CE7 9.17 5.51 19.63 1.06 54.22 4.52 2.26 22 8.71 5.23 18.65 1.011.77 54.22 4.52 2.26 5 23 8.44 5.07 18.06 0.98 2.83 54.22 4.52 2.26 8 248.25 4.96 17.66 0.96 3.54 54.22 4.52 2.26 10.01 25 7.79 4.68 16.68 0.95.3 54.22 4.52 2.26 14.98 CE8 9.17 5.5 19.63 1.06 54.22 4.52 2.26 268.71 5.23 18.65 1.01 1.77 54.22 4.52 2.26 5

The test results are reported as follows. For each test the average isreported followed by the standard deviation in parenthesis. The numberof samples utilized for each test is reported in the first row as “n”.

Diametral Stress, tensile um strength Flexural Flexural Compressivedeflection MPa strength, modulus, strength, (n = 2) (n = 4-6) MPa (n =6) MPa (n = 6) MPa (n = 5) CE7 4.14 63.3 (6.7) 127 (8.7) 7309 (146) 342(25.5) (0.49) 22 2.39 55.9 (8.6) 120 6157 339 (9.4) (0.05) 23 1.63 53.3(7.6) 103 (6.0) 5539 (77) 325 (10.8) (0.10) 24 1.55 62.8 (4.2) 101 (6.6)5187 (200) 338 (4.5) (0.03) 25 0.8) 59.7 (8.4)  86 (14.5) 3894 (198) 323(3.2) (0.03 CE8 4.19 Not Tested (0.19) 26 2.72 Not Tested (0.04)

In some embodiments, the dental compositions comprising conventionaldental monomers and addition fragmentation materials exhibited higherstress deflection results (e.g. >2.0) than Examples 1-20, comprising lowshrinkage monomer and addition fragmentation materials. However, theinclusion of an addition fragmentation material still substantiallyreduced the stress deflection in comparison to substantially the samecomposition lacking such addition fragmentation material.

Component Comparative Example 27 Example 28 Example 29 AFM-1 0.00 2.003.00 4.00 UDMA 7.60 7.45 7.37 7.30 HEMA 11.50 11.27 11.16 11.04 BisGMA3.80 3.72 3.69 3.65 BisEMA6 3.80 3.72 3.69 3.65 GDMA-P 11.60 11.37 11.2511.14 MEHQ 0.023 0.023 0.022 0.022 CPQ 0.115 0.113 0.112 0.110 EDMAB0.92 0.90 0.89 0.88 Irgacure 819 0.38 0.37 0.37 0.36 Zr/Si Filler 59.4058.21 57.62 57.02 Aerosil R812S 0.99 0.97 0.96 0.95Results

Compressive Diametral Adhesion Adhesion strength, tensile enamel, MPadentin, MPa MPa strength, MPa (Std. dev.) (Std. dev.) (Std. dev.) (Std.dev.) Comparative 9.4 (5.0) 11.9 (3.8)  345 (31) 80 (10) Example 27 11.3(1.2)  9.9 (2.6) 337 (20) 83 (4)  Example 28 Not tested Not tested 352(32) 81 (10) Example 29 8.5 (1.7) 6.5 (3.0) 369 (20) 77 (8) 

*Barcol *Barcol hardness, 2.0 mm, hardness, 2.0 mm, Stress, um top (Std.bottom deflection (Std. dev.) (Std. dev.) dev.) Comparative 78 (0) 78(0) 7.16 (0.11) Example 27 78 (0) 78 (0) 5.46 Example 28 78 (0) 78 (0)4.39 (0.20) Example 29 75 (1) 75 (1) 2.92 (0.15) *ELIPAR XL 3000 curinglight was used in place of the ELIPAR Freelight 2

What is claimed is:
 1. A dental composition comprising: anaddition-fragmentation agent of the formula:

wherein R¹, R² and R³ are each independently Z_(m)-Q-, a (hetero)alkylgroup or a (hetero)aryl group with the proviso that at least one of R¹,R² and R³ is Z_(m)-Q-; Q is a linking group have a valence of m+1; Z isan ethylenically unsaturated polymerizable group; m is 1 to 6; each X¹is independently —O— or —NR⁴—, where R⁴ is H or C₁-C₄ alkyl; and n is 0or 1; at least one monomer comprising at least two ethylenicallyunsaturated group; and inorganic oxide filler.
 2. The dental compositionof claim 1 wherein the addition-fragmentation agent comprises at leasttwo ethylenically unsaturated terminal groups.
 3. The dental compositionof claim 1 wherein the ethylenically unsaturated groups are(meth)acrylate groups.
 4. The dental composition of claim 1 wherein Zcomprises a vinyl, vinyloxy, (meth)acryloxy, (meth)acrylamido, styrenicand acetylenic functional groups.
 5. The dental composition of claim 1wherein Z is selected from:

wherein R⁴ is H or C₁-C₄ alkyl.
 6. The dental composition of claim 1wherein Q is selected from —O—, —S—, —NR⁴—, —SO₂—, —PO₂—, —CO—, —OCO—,—R⁶—, —NR⁴—CO—NR⁴—, NR⁴—CO—O—, NR⁴—CO—NR⁴—CO—O—R⁶—, —CO—NR⁴—R⁶—,—R⁶—CO—O—R⁶—, —O—R⁶—, —S—R⁶—, —NR⁴—R⁶—, —SO₂—R⁶—, —PO₂—R⁶—, —CO—R⁶—,—OCO—R⁶—, —NR⁴—CO—R⁶—, NR⁴—R⁶—CO—O—, and NR⁴—CO—NR⁴—, wherein each R⁴ ishydrogen, a C₁ to C₄ alkyl group, or aryl group, each R⁶ is an alkylenegroup having 1 to 6 carbon atoms, a 5- or 6-membered cycloalkylene grouphaving 5 to 10 carbon atoms, or a divalent arylene group having 6 to 16carbon atoms, with the proviso that Q-Z does not contain peroxidiclinkages.
 7. The dental composition of claim 1 wherein Q is an alkyleneor hydroxyl-substituted alkylene or aryloxy-substituted alkylene oralkoxy-substituted alkylene.
 8. The dental composition of claim 1wherein Q is an alkylene of the formula —C_(r)H_(2r)—, where r is 1 to10.
 9. The dental composition of claim 1 wherein Q is ahydroxyl-substituted alkylene.
 10. The dental composition of claim 1wherein Q is —CH₂—CH(OH)—CH₂—.
 11. The dental composition of claim 1wherein Q is an aryloxy-substituted alkylene.
 12. The dental compositionof claim 1 wherein R⁵ is an alkoxy-substituted alkylene.
 13. The dentalcomposition of claim 1 wherein R¹—X¹— groups (and optionally R²—X²—groups) is selected from H₂C═C(CH₃)C(O)—O—CH₂—CH(OH)—CH₂—O—,H₂C═C(CH₃)C(O)—O—CH₂—CH(O—(O)C(CH₃)═CH₂)—CH₂—O—,H₂C═C(CH₃)C(O)—O—CH(CH₂OPh)—CH₂—O—,H₂C═C(CH₃)C(O)—O—CH₂CH₂—N(H)—C(O)—O—CH(CH₂OPh)—CH₂—O—,H₂C═C(CH₃)C(O)—O—CH₂—CH(O—(O)C—N(H)—CH₂CH₂—O—(O)C(CH₃)C═CH₂)—CH₂—O—,H₂C═C(H)C(O)—O—(CH₂)₄—O—CH₂—CH(OH)—CH₂—O—,H₂C═C(CH₃)C(O)—O—CH₂—CH(O—(O)C—N(H)—CH₂CH₂—O—(O)C(CH₃)C═CH₂)—CH₂—O—,CH₃—(CH₂)₇—CH(O—(O)C—N(H)—CH₂CH₂—O—(O)C(CH₃)C═CH₂)—CH₂—O—,H₂C═C(H)C(O)—O—(CH₂)₄—O—CH₂—CH(—O—(O)C(H)═CH₂)—CH₂—O— andH₂C═C(H)C(O)—O—CH₂—CH(OH)—CH₂—O—,H₂C═C(H)C(O)—O—(CH₂)₄—O—CH₂—CH(—O—(O)C(H)═CH₂)—CH₂—O—, andCH₃—(CH₂)₇—CH(O—(O)C—N(H)—CH₂CH₂—O—(O)C(CH₃)C═CH₂)—CH₂—O—.
 14. Thedental composition of claim 1 wherein the ethylenically unsaturatedgroups of the monomer are (meth)acrylate groups.
 15. The dentalcomposition of claim 1 wherein the monomer is an aromatic monomer havinga refractive index of at least 1.50.
 16. The dental composition of claim1 wherein the monomer is a low volume shrinkage monomer.
 17. The dentalcomposition of claim 1 wherein the monomer is an isocyanurate monomer, atricyclodecane monomer, or a mixture thereof.
 18. The dental compositionof claim 1 wherein the hardened dental composition exhibits a stressdeflection no greater than 2.0.
 19. The dental composition of claim 1wherein the dental composition comprises at least one (meth)acrylatemonomer selected from ethoxylated bisphenol A dimethacrylate (BisEMA6),2-hydroxyethyl methacrylate (HEMA), bisphenol A diglycidyldimethacrylate (bisGMA), urethane dimethacrylate (UDMA), triethlyeneglycol dimethacrylate (TEGDMA), glycerol dimethacrylate (GDMA),ethylenegylcol dimethacrylate, neopentylglycol dimethacrylate (NPGDMA),polyethyleneglycol dimethacrylate (PEGDMMA), and mixtures thereof. 20.The dental composition of claim 1 wherein the filler inorganic oxidefiller comprises nanoparticles.
 21. The dental composition of claim 20wherein the inorganic nanoparticles comprise silica, zirconia, ormixtures thereof.
 22. The dental composition of claim 20 wherein theinorganic nanoparticles are in the form of nanoclusters.
 23. A method oftreating a tooth surface, the method comprising providing a hardenabledental composition of claim 1 comprising an addition-fragmentationagent, placing the dental composition on a tooth surface; and hardeningthe hardenable dental composition.
 24. The method of claim 23 whereinthe dental composition further comprises at least one ethylenicallyunsaturated monomer with acid functionality.
 25. A dental articlecomprising the hardenable dental composition of claim 22 at leastpartially hardened.
 26. A method of treating a tooth surface, the methodcomprising providing an at least partially hardened dental articleaccording to claim 25, adhering the dental article on a tooth surface inthe mouth of a subject.
 27. The dental composition of claim 1 furthercomprising a redox hardening agent.